Diet, Nutrition, and Cancer
Committee on Diet, Nutrition, and Cancer
Assembly of Life Sciences
National Research Council
NATIONAL ACADEMY PRESS
Washington, D.C. 1982
NOTICE: The project that is the subject of this report was approved by
the Governing Board of the National Research Council, whose members are
drawn from the Councils of the National Academy of Sciences, the National
Academy of Engineering, and the Institute of Medicine* The members of
the committee responsible for the report were chosen for their special
competences and with regard for appropriate balance.
This report has been reviewed by a group other than the authors
according to procedures approved by a Report Review Committee consist-
ing of members of the National Academy of Sciences, the National Academy
of Engineering, and the Institute of Medicine.
The National Research Council was established by the National
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and the National Academy of Engineering in the conduct of their services
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Medicine were established in 1964 and 1970, respectively, under the
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COMMITTEE ON DIET, NUTRITION, AND CANCER 1
CLIFFORD GROBSTEIN, Chairman
JOHN CAIRNS, Vice Chairman
ROBERT BERLINER
SELWYN A. BROITMAN
T. COLIN CAMPBELL
JOAN D. GUSSOW
LAURENCE N. KOLONEL
DAVID KRITCHEVSKY
WALTER MERTZ
ANTHONY B. MILLER
MICHAEL J. PRIVAL
THOMAS SLAGA
LEE WATTENBERG
TAKASHI SUGIMURA, Advisor
National Research Council Staff;
SUSHMA PALMER, Project Director
KULBIR BAKSHI, Staff Officer
LESLIE J. GRAYBILL, Research Associate
ROBERT HILTON, Research Associate
FRANCES M. PETER, Editor
Appendix A for further information on committee members and staff.
PREFACE
Heightened interest in reducing the risk of three of the most
dreaded diseases heart disease, cancer, and stroke has resulted in
periodic efforts to "improve 11 food habits* These efforts attracted
national attention during the last decade when a White House confer-
ence and congressional hearings explored the state of our knowledge
concerning the status and health effects of nutrition in the United
States. During the hearings there were inquiries about the relative
emphasis placed on nutritional factors in the research strategy of
the National Cancer Institute (NCI). The study described in this
report is an outgrowth of these inquiries*
In June 1980, the NCI commissioned the National Research Council
(NRC) to conduct a comprehensive study of the scientific information
pertaining to the relationship of diet and nutrition to cancer. The
NCI requested that the study committee (1) "review ... the state of
knowledge and information pertinent to diet/nutrition and the incidence
of cancer"; (2) "develop a series of recommendations related to dietary
components (nutrients and toxic contaminants) and nutritional factors
which can be communicated to the public"; and (3) "based on the above
state-of-the-art appraisals and the identification of gap areas > de-
velop a series of research recommendations related to dietary compo-
nents and nutritional factors and the incidence of cancer." The agency
also asked that two reports be prepared: the first to advise the NCI
and the public whether evidence indicates that certain dietary habits
may affect the risk of developing cancer and the second to inform NCI
and the scientific community about useful directions research might
take to increase our knowledge in this area. The first report is con-
tained in this volume. It summarizes the most relevant scientific
information on diet and cancer and recommends several interim dietary
guidelines for dissemination to the public. In the second report,
which is expected to be completed in approximately 1 year, the com-
mittee will consider potentially profitable areas for future research.
The NRC Governing Board assigned administrative responsibility
for this project to the Executive Office of the Assembly of Life
Sciences (ALS). Subsequently, a 13-member committee and one advisor
were appointed to conduct the study* The diverse expertise repre-
sented on the committee includes such disciplines as biochemistry,
microbiology, embryology, epidemiology, experimental oncology, in-
ternal medicine, microbial genetics, molecular biology, molecular
genetics, nutrition, nutrition education, public health, and toxi-
cology* Institutional affiliations and major research interests of
the committee members and the staff are presented in Appendix A at
the end of this report. This multidlsclplinary composition has served
to ensure comprehensive coverage, of the scientific literature and to
provide a broad perspective to the committee's conclusions. The work
of the committee has been aided by extensive consultation with sci-
entific colleagues, by specially arranged technical conferences on
specific subjects, and by a public meeting to receive such additional
Information and advice as scientists and others wished to provide.
Food, nutrition, diet, and cancer are terms that encompass a very
broad subject area, and the already vast accumulation of literature
on the interrelationship of these factors is growing rapidly. Thus,
the committee began its work by developing a preliminary map of its
"territory." Having initially interpreted its charge to mean that no
part should be arbitrarily excluded, the committee came to recognize
that it would be wasteful to duplicate effort, especially when certain
subjects have recently been evaluated in detailed reviews. After
careful consideration, the decision was made to refer the reader to
these comprehensive reviews and to concentrate in this report on the
relationship between diet and its nutritional components and cancer in
a narrower sense. Subjects not covered in detail include the health
effects of nitrate, nitrite, and N-nitroso compounds, which have recent-
ly been studied by another ALS committee, and drinking water a carrier
of nutrients and potential toxic substances also examined by an ALS
committee. The Committee on Diet, Nutrition, and Cancer evaluated the
evidence for selected contaminants and food additives, but did not dis-
cuss them in detail because the emphasis in this report is placed on
the selection of particular foods or dietary regimens made by individ-
uals or population groups, and the significance of these choices for
cancer incidence.
During its preliminary mapping of territory, the committee recog-
nized that its charge does not include the evaluation of diet and nu-
trition in relation to cancer therapy, but rather it stipulated that
the committee's effort be directed toward the assessment of these
factors in the etiology and prevention of cancer.
The committee is aware that several aspects of its charge are
matters of controversy, either within the scientific and medical com-
munity or among the general population. Controversies are inevitable
when data are neither clear-cut nor complete. Interpretations then
depend on the criteria selected for evaluation and are influenced by
individual or collective judgment. The committee has attempted to
present the evidence as objectively as possible and to indicate the
range of scientifically acceptable interpretation. It hopes that the
results will be useful to all interested parties. The charge to the
committee also included a request for dietary recommendations that
could be used in the formulation of public policy. Although the com-
mittee decided that the data base is not yet adequate for firm recom-
mendations to be made, it did conclude that there was sufficient justi-
fication for certain interim guidelines, which are presented in the
Executive Summary (Chapter 1) of this report.
Scientifically valid data on diet and nutrition in relation to
cancer are provided by three major sources: epidemiological studies on
human populations; experimental studies on animals; and in vitro tests
for genetic toxicity. All three types of studies provide useful in-
formation, especially when data derived from all sources point in
the same direction. Accordingly, after a general introduction, this
report presents the epidemiological and laboratory evidence for indi-
vidual components of the diet, giving special attention to the degree
of concordance between the epidemiological and experimental evidence.
Nutrients are reviewed in Section A, and nonnutritive components are
reviewed in Section B. Because of the great interest in the possible
etiological and preventive roles of the dietary factors reviewed in
Section B, a separate chapter is devoted to constituents that may act
as inhibitors of carcinogenesis.
The trends in cancer incidence have been the subject of intense
public interest and constant debate among scientists. Although this
report does not purport to examine this issue in detail, Section C
(Chapters 16 and 17) summarizes the current state of knowledge while
focusing on the role that diet plays in the incidence of cancer at
specific sites. Chapter 18 describes a framework for risk assessment
with particular attention to the nuances that must be taken into
account when quantifying the effects of so complex a mixture as diet.
In the Executive Summary (Chapter 1) , the committee has assembled
a general picture of the role of dietary and nutritional factors in
the development and prevention of cancer from the detailed information
presented in other chapters. The report concludes with a glossary of
technical terms.
The committee particularly wishes to commend the able and devoted
assistance of an NRC staff headed by Dr. Sushma Palmer, and consisting
of Dr. Kulbir Bakshl, Mrs. Frances Peter, Mrs. Leslie Graybill, Mr.
Robert Hilton, Mrs. Susan Barron, Mrs. Dena Banks, and Mrs. Eileen
Brown.
The committee is also greatly indebted to Drs. Kenneth D. Fisher
and Richard G. Allison from the Federation of American Societies for
Experimental Biology; Dr. Michael Kazarinoff from Cornell University;
Dr. Dietrich Knorr from the University of Delaware; Dr. Angela Little
from the University of California at Berkeley; and Dr. Leonard Stoloff
of the Food and Drug Administration, who served as consultants and in
this capacity wrote manuscripts for the consideration and use of the
committee, and extends thanks to those who gave testimony at the public
meeting or, upon request, presented data and engaged in discussions
during committee meetings, conferences, or workshops. Many others,
especially Drs. Willard Visek, Kenneth Carroll, Morris Ross, Juanell
Boyd, Joseph Rodricks, and Elizabeth Weisburger, also provided valua-
ble advice to the committee from time to time.
Furthermore, the committee is grateful to Drs. Andrew Chiarodo
and Diane Fink, the current and former project officers for this study
at NCI, for their continuous interest and support; to Drs. Alvin G.
Lazen and Robert Tardiff of the NRC staff; to members of the Board
on Toxicology and Environmental Health Hazards for their advice in the
planning of this study; to Ms. Barbara Jaffe, Miss Virginia White, and
the staff of the Toxicology Information Center for their assistance and
cooperation in supplying bibliographic material; to Ms. Estelle Miller
and her coworkers at the NRG Manuscript Processing Unit; and to Mrs.
Cecil Read, Mrs. Barbara Wensus, Mrs. Barbara Smith, and Mrs. Ute
Hayman for their constant support in the preparation of the report.
CLIFFORD GROB STEIN
Chairman
Committee on Diet, Nutrition, and Cancer
CONTENTS
CHAPTER 1 - EXECUTIVE SUMMARY .................... . ............. 1-1
Summary and Conclusions ............................ 1-3
Dietary Patterns and Components of Food ......... 1-3
Total Caloric Intake ............................ 1-3
Lipids (Fats and Cholesterol) ................... 1-4
Protein ......................................... 1-5
Carbohydrates. . ........ ......... ................ 1-6
Dietary Fiber ................................... 1-6
Vitamins ................... . .................... 1-7
Minerals ........................................ 1-9
Inhibitors of Carcinogenesis .................. .1-11
Alcohol ......................................... 1-11
Naturally Occurring Carcinogens. ........ ...... . .1-12
Mutagens in Foods ............................... 1-12
Food Additives ................... . .............. 1-13
Environmental Contaminants ....... ...... ........ .1-13
Contribution of Diet to Overall Risk of Cancer.. 1-14
Interim Dietary Guidelines ..................... ... .1-14
CHAPTER 2 - CANCER: ITS NATURE AND RELATIONSHIP TO DIET ....... 2-1
The Nature of Cancer ..... . ...... . . ................. 2-1
The Control of Cell Division During the
Growth and Replacement of Normal Tissues ..... .2-1
Various Abnormalities of Cell Behavior ....... ...2-2
Cancer and Cell Heredity ..... ................... 2-3
The Varying Incidence of Cancer ........... ..... 2-4
Experimentally Induced Carcinogenesis ........... 2-5
The Causes of Cancer ... . . . . ....... .............. 2-7
The Influence of Diet on Experimentally Induced
Cancers .................... ........ *** ....... 2-10
The Early Stages of Carcinogenesis .............. 2-10
The Late Stages of Carcinogenesis ............ ...2-11
References ......................................... 2-13
CHAPTER 3 - METHODOLOGY ................................. ....... 3-1
Epidemiological Methods .............. * ........... 3-2
CONTENTS
Page
General Approaches 3-2
Methods for Determining Dietary Intake 3-3
Overall Assessment of Epidemiological
Approaches 3-8
Laboratory Methods 3-9
Analysis of Molecular Structure 3-9
Short-Term Tests 3-10
Long-Term Bioassays 3-11
Difficulties in Studying the Carcinogenicity
and Mutagenicity of Food Constituents 3-12
Committee's Approach to Evaluation of the
Literature 3-14
Summary and Conclusions * 3-15
References . . 3-18
SECTION A - THE RELATIONSHIP BETWEEN NUTRIENTS AND CANCER A-l
Changes in the Food Supply A-l
Summary and Conclusions A-l 2
References A-l 4
CHAPTER 4 - TOTAL CALORIC INTAKE 4-1
Epidemiological Evidence 4-1
Experiment s in Animals 4-3
Summary and Conclusions 4-4
Epidemiological Evidence 4-4
Experimental Evidence 4-4
References * 4-6
CHAPTER 5 - LIPIDS (FATS AND CHOLESTEROL) 5-1
Epidemiological Evidence 5-1
Fats 5-1
Cholesterol* 5-5
CONTENTS
Page
Relationship of Fecal Steroid Excretion to Bowel
Carcinogenesis 5-9
Experimental Evidence 5-11
Mammary Tumors 5-11
Hepatic and Pancreatic Cancer 5-14
Intestinal Cancer 5-15
Summary - . . ....... 517
Epidemiological Evidence 5-17
Relationship of Fecal Steroid Excretion to
Bowel Carcinogenesis 5-18
Experimental Evidence 5-19
Conclusions 5-20
References * 5-22
CHAPTER 6 - PROTEIN 6"" 1
Epidemiological Evidence. ... * 6-1
Breast Cancer 6-1
Large Bowel Cancer 6-2
Pancreatic Cancer * 6-3
Other Cancers 6-4
Experimental Evidence 6-4
Spontaneous Tumors 6-6
Chemically Induced Tumors 6-7
Tumor Transplantation Studies 6-10
An Evaluation of the Data from Animal Studies. . .6-10
Summary
EpidemiQlogical Evidence 6-11
Experimental Evidence 6-11
Conclusion. .. * * o-ll
References 6 ~
CONTENTS
Page
CHAPTER 7 - CARBOHYDRATES 7-1
Epidemiological Evidence 7-1
Experimental Evidence 7-2
Sucrose * 7-2
Lactose 7-3
Glucose 7-3
Xylitol 7-3
Summary * 7-4
Epidemiological Evidence 7-4
Experimental Evidence 7-4
Conclusion 7-5
References * 7-6
CHAPTER 8 - DIETARY FIBER 8-1
Epidemiological Evidence *** 8-1
Experimental Evidence 8-3
Summary 8-5
Epidemiological Evidence 8-5
Experimental Evidence 8-5
Conclusion 8-5
References 8-6
CHAPTER 9 - VITAMINS 9-1
Vitamin A 9-1
Epidemiological Evidence 9-1
Experimental Evidence 9-4
Summary .9-6
Conclusion 9-7
Vitamin C (Ascorbic Acid) 9-7
Epidemiological Evidence . . 9-7
Experimental Evidence 9-8
CONTENTS
Page
Summary .................................. . ...... 9-10
Conclusion ...................................... 9-10
Vitamin E (ot-Tocopherol) ....... . .............. ..... 9-10
Epidemiological Evidence ........................ 9-10
Experimental Evidence ........................... 9-10
Summary and Conclusions .................... ..... 9-12
Choline and Selected B Vitamins .................... 9-12
Epidemiological Studies ................. * ....... 9-13
Experimental Studies ............................ 9-13
Summary and Conclusions ......................... 9-15
References ........ ................................. 9-16
CHAPTER 10 - MINERALS .......................................... 10-1
Selenium ........................................... 10-2
Epidemiological Evidence .......... ...... ........ 10-2
Experimental Evidence .................... ..... .10-3
Summary * ........ ...... ....... ......... .......... 107
Conclusion ........................ ............. 10-7
Zinc ............................................... 10-8
Epidemiological Evidence. . ...................... 10-8
Experimental Evidence. . . ........................ 10-9
Summary. . . ...................................... 10-10
Conclusion. . ........................ ............ 10-11
Iron.
Epidemiological Evidence ..... . .................. 10-11
Experimental Evidence ....... ............ ........ 10 I 12
Summary ..... ....... .............. ........ ...... 10 12
Conclusion. ..*...*. ..... .......... ..... . ........ 10-12
10-12
Epidemiological Evidence ..... ................... 10-13
Experimental Evidence. . . ..... .................. 10-14
Summary ...................................... - 10 " 14
Conclusion ............................. ------- ..... 10-14
CONTENTS
Iodine 10-14
Epidemiological Evidence 10-15
Experimental Evidence 10-16
Summary 1016
Conclusion 10-17
Molybdenum 10-17
Epidemiological Evidence 10-17
Experimental Evidence 10-17
Summary .... .1018
Conclusion. 10-18
Cadmium 10-18
Epidemiological Evidence 10-18
Experimental Evidence 10-19
Summary 10-19
Conclusion 10-20
Arsenic 10-20
Epidemiological Evidence 10-21
Experimental Evidence 10-21
Summary and Conclusions 10-22
Lead 10-23
Epidemiological Evidence 10-23
Experimental Evidence 10-23
Summary 10-24
Conclusion 10-25
References 10-26
CHAPTER 11 - ALCOHOL 11-1
Epidemiological Evidence 11-1
Specific Alcoholic Bey^rages . . 11-1
Total Alcoholic Beverages .11-2
Synergism Between Alcohol and Smoking. , .11-4
Effect of Nutritional Status* 11-5
CONTENTS
Page
Experimental Evidence 11-5
Postulated Mechanisms of Action in Carcino-
genesis 11-5
Alcohol and Induction of Microsomal Enzymes 11-6
Occurrence of Putative Carcinogens in Alcoholic
Beverages 11-6
Summary and Conclusions 11-7
References 11-8
SECTION B - THE ROLE OF NONNUTRITIVE DIETARY CONSTITUENTS B-l
Food Additives B-l
Contaminants . B-2
The Delaney Clause and Other Regulatory Actions* . *.B-3
Exposure of Humans. . * B-6
The Carcinogenicity of Food Additives and Con-
taminants .B-8
Assessment of Effects on Human Health** B-l 2
References B-13
CHAPTER 12 - NATURALLY OCCURRING CARCINOGENS 12-1
Mycotoxins. 12-1
Af latoxins 12-2
Other Mycotoxins 12-5
Summary and Conclusion: Af la toxins and Other
Mycotoxins. 12-5
Hydrazines in Mushrooms . * 12-7
Agaricus bisporus. .......... * . . . . .12-7
Gyromitra esculenta . . . * 12-8
Summary and Conclusions: Hydrazines 12-9
Plant Constituents and Metabolites 12-9
CONTENTS
/
Page
Pyrrolizidine Alkaloids 12-9
Allylic and Propenylic Benzene Derivatives 12-10
Bracken Fern Toxin(s) 12-11
Estrogenic Compounds* . . 12-12
Coffee 12-13
Methylxanthines 12-14
Cycasin 12-15
Thiourea . 12-15
Tannic Acid and Tannins 12-16
Coumarin ........ 12-16
Parasorbic Acid 12-17
Metabolites of Animal Origin 12-17
Tryptophan and Its Metabolites 12-17
Hormones 12-18
Fermentation Product 12-18
Ethyl Carbamate (Urethan) 12-18
Nitrate, Nitrite, and N-Nitroso Compounds 12-19
Epidemlological Evidence 12-20
Experimental Evidence: Carcinogenlcity 12-21
Experimental Evidence: Mutageniclty 12-23
Summary and Conclusions: Nitrate, Nitrite,
and N-Nitroso Compounds * .12-23
Summary and Conclusions .12-24
References. 12-26
CHAPTER 13 - MUTAGENS IN FOOD 13-1
Mutagens Resulting from Cooking of Foods 13-2
Benzo[a]pyrene and Other Polynuclear Aromatic
Hydrocarbons .13-2
Mutagens from Pyrolyzed Proteins and Amlno
Acids .,*.*.... .13-3
Mutagens Formed from Meat at Lower fempera^
tures 13-8
Mutagen Formation Involving Carbohydrates 13-9
Plant Flavonoids. . ...... . . . *, 13-10
Mutagenic Activity in Extracts of Foods and
Beverages 13-11
CONTENTS
Page
Modifiers of Mutagenic Activity 13-12
Harman and Norharman . 13-13
Hemin 13-14
Fatty Acids 13-14
Ni trite 13-14
Antioxidants 13-15
Summary and Conclusions 13-16
References 13-17
CHAPTER 14 - ADDITIVES AND CONTAMINANTS 14-1
Additives 14-1
Saccharin 14-1
Cyclamates 14-5
Aspartame 14-7
Butylated Hydroxytoluene (BHT) and Butylated
Hydroxyanisole (BHA) 14-8
Vinyl Chloride 14-10
Acrylonitrile . 14-12
Diethylstilbestrol (DES) . .14-13
Environmental Contaminants 14-14
Pesticides 14-14
Poly chlorinated Biphenyls (PCB f s) 14-22
Polybrominated Biphenyls (PBB 1 s) 14-25
Polycyclic Aromatic Hydrocarbons (PAH's) 14-25
Overall Summary and Conclusions. 14-29
Food Additives. . . . . 14-29
Environmental Contaminants . .14-29
References. . . 14-30
CHAPTER 15 - INHIBITORS OF CARCINOGENESIS 15-1
Epidemiological Studies. . . . 15-1
Experimental Studies . . . ... 15-2
Effects of Selected Chemicals* .. . * ... . * 15-2
CONTENTS
Page
Modifiers of Mutagenic Activity ................... 13-12
Harman and Norharman ........................... 13-13
Hemin .......................................... 13-14
Fatty Acids .................................... 13-14
Nitrite ........................................ 13-14
Antioxidants ................................... 13-15
Summary and Conclusions ........................... 13-16
References ........................................ 13-17
CHAPTER 14 - ADDITIVES AND CONTAMINANTS ....................... 14-1
Additives ......................................... 14-1
Saccharin
Cyclamates
14-5
Aspartame 14-7
Butylated Hydroxytoluene (BHT) and Butylated
Hydroxyanlsole (BHA) 14-8
Vinyl Chloride 14-10
Acrylonitrile 14-12
Diethylstilbestrol (DES) 14-13
Environmental Contaminants 14-14
Pesticides 14 -1 4
Polychlorinated Biphenyls (PCB's) 14-22
Polybrominated Biphenyls (PBB f s ) 14-25
Polycyclic Aromatic Hydrocarbons (PAH's) 14-25
Overall Summary and Conclusions 14-29
Food Additives 14-29
Environmental Contaminants * 14-29
Reference s 4-
CHAPTER 15 - INHIBITORS OF CARCINOGENESIS. 15-1
Epidemiological Studies. 1 5 ~1
Experimental Studies. . ..... * * * I 5 "" 2
Effects of Selected Chemicals .. ..... . . . .15-2
CONTENTS
Effects of Individual Foods on Carcinogen-
Metabolizing Enzyme Systems 15-7
Possible Adverse Effects of Inhibitors 15-8
Summary. .15-9
Epidemiological Studies 15-9
Experimental Studies 15-9
Conclusion 15-9
References 15-10
SECTION C - PATTERNS OF DIET AND CANCER C-l
CHAPTER 16 - CANCER INCIDENCE AND MORTALITY 16-1
Geographical Differences Related to Ethnicity 16-1
Changes Subsequent to Migration* 16-3
Changing Time Trends in Incidence and Mortality. . .16-5
Intersite Correlations of Incidence 16-7
Associations with Socioeconomic Status 16-8
Religious Practices and Cancer Incidence and
Mortality 16-10
Correlations of Incidence and Mortality with
Dietary and Other Variables 16-11
Associations with Other Diseases .....16-13
Summary 16-13
References 16-14
CHAPTER 17 - THE RELATIONSHIP OF DIET TO CANCER AT SPECIFIC
SITES ..*,.. 17-1
Esophageal Cancer .17-1
Stomach Cancer . .... .17-3
Colon and Rectal Cancer . * . . . * ... .17-6
CONTENTS
Page
Liver Cancer 17-11
Pancreatic Cancer 17-12
Gallbladder Cancer 17-14
Lung Cancer 17-14
Bladder Cancer 17-15
Renal Cancer . 17-16
Breast Cancer 17-17
Endometrial Cancer 17-19
Ovarian Cancer .17-19
Prostate Cancer 17-20
References 17-22
CHAPTER 18 - ASSESSMENT OF RISK TO HUMAN HEALTH 18-1
Initiators of Carcinogenesis 18-2
Modifiers of Carcinogenesis 18-5
Use of Mutagenicity Tests 18-6
Use of Epidemiological Studies 18-7
Diet-Related Carcinogenesis 18-8
Contribution of Diet to Overall Risk of Cancer. .. .18-10
References. . . . 18-12
GLOSSARY G-l
APPENDIX A - COMMITTEE ON DIET, NUTRITION, AND CANCER-
AFFILIATIONS AND MAJOR RESEARCH INTERESTS A-l
CHAPTER 1
EXECUTIVE SUMMARY
Scientific pronouncements are usually viewed by the public as carry-
ing a rather high level of certainty. Therefore, scientists must be
especially careful in their choice of words whenever they are not total-
ly confident about their conclusions. For example, it has become abso-
lutely clear that cigarettes are the cause of approximately one-quarter
of all the fatal cancers in the United States. If the population had
been persuaded to stop smoking when the association with lung cancer was
first reported, these cancer deaths would now not be occurring. Twenty
years ago the "stop-smoking" message required some rather cautious word-
ing. Today, the facts are clear, and the choice of words is not so
important.
The public often demands certain kinds of information before such
information can be provided with complete certainty. For example,
weather forecasting is often not exact; nevertheless, the public asks
that the effort be made, but has learned to accept the fact that the
results are not always reliable.
The public is now asking about the causes of cancers that are not
associated with smoking. What are these causes, and how can these
cancers be avoided? Unfortunately, it is not yet possible to make firm
scientific pronouncements about the association between diet and cancer.
We are in an interim stage of knowledge similar to that for cigarettes
20 years ago. Therefore, in the judgment of the committee, it is now
the time to offer some interim guidelines on diet and cancer.
Approximately 20% of all deaths in the United States are caused by
cancer. Although the number of cancer cases is steadily increasing as
the population grows, the ^ge-ad justed total cancer incidence and mor-
tality rates for sites other than the respiratory tract (cancers of
which are primarily due to cigarette smoking) have as a whole remained
stable during the last 30 to 40 years.
The search for the causes of cancer has been an important branch of
cartcer research. Considerable effort has been devoted to studying the
influence of both environmental and genetic factors on the incidence of
cancer. In the course of this research, it has become clear that most
cancers have external causes and, in principle, should therefore be pre-
ventable. For example, blacks and Japanese residing in the United States
develop the spectrum of cancers that is typical for the United States but
different from that In Africa and Japan.
But what might these external causes be? Many factors in our en-
vironment are potential causes of cancer, they include substances in
the air we breathe, the water we drink, the regions in which we work and
1-2
live, and the foods we eat. Our exposure to some of these factors var-
ies in ways that can be precisely measured. For most factors, however,
the measurement of the exposures and the assessment of their effects are
neither precise nor straightforward. Among the factors whose precise
effects are difficult to assess are the diets consumed by different
groups of people. The measurements are difficult not only because it is
hard to learn what people eat but also because the foods comprising
their diets are so complex.
Studies of the association between diet and cancer have focused on
cancers of the gastrointestinal tract, the breast and other tissues
susceptible to hormonal influence, and, to a lesser extent, the respi-
ratory tract and the urinary bladder. After assessing the resultant
literature, the committee concluded that the differences in the rates
at which various cancers occur in different human populations are often
correlated with differences in diet. The likelihood that some of these
correlations reflect causality is strengthened by laboratory evidence
that similar dietary patterns and components of food also affect the
incidence of certain cancers in animals.
Chapters 16 and 17 provide information about the trends in cancer
incidence and the relationship between diet and the incidence of cancer
at specific sites.
Epidemiologists have found it relatively easy to demonstrate a cor-
relation between diets consumed in modern affluent societies and the
incidence of cancers in such organs as the breast, colon, and uterus.
But it has proved to be much more difficult to establish causal rela-
tionships and to determine which, if any, of the dietary components is
responsible.
Similarly, difficulties are encountered in laboratory experiments.
Like humans, most animals have a significant incidence of cancer in old
age, and the rates of these cancers often tend to be affected by changes
in diet. However, the influence of diet on spontaneous and experimen-
tally induced cancers is not easily investigated because the underlying
mechanisms and molecular biology of the cancers are still not fully
understood. Indeed, the effects of diet were often regarded as a
nuisance i.e., yet another variable standing between the investigators
and their measurement of carcinogenic! ty. As a consequence, researchers
have only recently returned to the study of diet as a factor in carcino-
genesis.
It is possible that research in progress will generate more defini-
tive information that will be useful in formulating dietary recommenda-
tions to minimize the risk of cancer. In the meantime, the committee
believes that the evidence at hand justifies certain interim guidelines.
These guidelines appear at the end of this chapter following a summary
of the committee's findings and the conclusions it believes dan be drawn
from the scientific evidence.
1-3
SUMMARY AND CONCLUSIONS
Dietary Patterns and Components of Food
Since the turn of the century, new methods of processing and storage
have resulted in a proliferation of the kinds and numbers of food items
available to the U.S. population. Unfortunately, little is known about
the ways in which such innovations have altered the specific composition
of the diet. The only components of food that have been monitored regu-
larly are the nutrients. The dietary levels of most nutrients have
changed relatively little over the past 80 years.
Attempting to determine which constituents of food might be associ-
ated with cancer, epidemiologists have studied population subgroups,
including migrants to the United States, to examine the relationship
between specific dietary patterns or the consumption of certain foods
and the risk of developing particular cancers. In general, the evidence
suggests that some types of diets and some dietary components (e.g.,
high fat diets or the frequent consumption of salt-cured, salt-pickled,
and smoked foods) tend to increase the risk of cancer, whereas others
(e.g., low fat diets or the frequent consumption of certain fruits and
vegetables) tend to decrease it. The mechanisms responsible for these
effects are not fully understood, partly because nutritive and non-
nutritive components of foods may interact to exert effects on cancer
incidence.
In the laboratory, investigators have attempted to shed light on the
mechanisms by which diet may influence carcinogenesis. They have ex-
amined the ability of Individual nutrients, food extracts, or non-
nutritive components of food to enhance or inhibit carcinogenesis and
mutagenesis, thereby providing epidemiologists with testable hypotheses
regarding specific components of the diet. Because the data from both
types of studies are generally grouped according to dietary constitu-
ents, the committee found it advantageous to organize its report in a
similar fashion.
Total Caloric Intake
The committee reviewed many studies in which the variable examined
was the total amount of food consumed by humans or animals, rather than
the precise composition of the diet. This review is contained in
Chapter 4, which is entitled "Total Caloric Intake," even though the
studies did not indicate whether the observed effects resulted from the
changes in the proportion of specific nutrients in the diet or from the
modification of total caloric intake.
Since very few epidemiologists have been able to examine the effect
of caloiric intake per se on the risk of cancer, their reports have pro-
vided largely indlrect^evidence for such a relationship, and much of it
is based on associations between body weight or obesity and cancer.
In laboratory experiments, the incidence of tumors is lower and the
lifespan much longer for animals on restricted food intake than for ani-
mals fed ad libitum. However, because the intake of all nutrients was
simultaneously depressed in these studies, the observed reduction in
tumor incidence might have been due to the reduction of some specific
nutrient, such as fat. It is also difficult to Interpret experiments In
which caloric Intake has been modified by varying dietary fat or fiber,
both of which may by themselves exert effects on tumorlgenesis.
Thus, the committee concluded that neither the epidemiological stud-
ies nor the experiments in animals permit a clear interpretation of the
specific effect of total caloric intake on the risk of cancer. Nonethe-
less, the studies conducted in animals show that a reduction in total
food Intake decreases the age-specific Incidence of cancer. The evi-
dence Is less clear for human beings.
Lipids (Fats and Cholesterol)
Many epidemiological and laboratory studies have been conducted to
examine the association between cancer and intake of lipids, i.e., total
dietary fat, saturated fat, polyunsaturated fat, and cholesterol.
Fats. Epidemiological studies have repeatedly shown an association
between dietary fat and the occurrence of cancer at several sites, espe-
cially the breast, prostate, and large bowel. In various populations,
both the high incidence of and mortality from breast cancer have been
shown to correlate strongly with higher per capita fat consumption; the
few case-control studies conducted have also shown this association with
dietary fat. Like breast cancer, increased risk of large bowel cancer
has been associated with higher fat Intake in both correlation and case-
control studies. The data on prostate cancer are more limited, but they
too suggest that an increased risk Is related to high levels of dietary
fat. In general, it Is not possible to identify specific components of
fat as being clearly responsible for the observed effects, although
total fat and saturated fat have been associated most frequently.
The epidemiological data are not entirely consistent. For example,
the magnitude of the association of fat with breast cancer appears
greater in the correlation data than in the case-control data, and
several reports on large bowel cancer fail to show an association with
fat. Possible reasons for these discrepancies are apparent . These are
discussed in Chapter 5 (see pages 5-5 and 5-18).
Like epidemiological studies, numerous experiments in animals have
shown that dietary lipids Influence tuti*origenesls, especially IB the
breast and the colon. An increase In fat intake from 5% to 20% of the
weight of the diet (i.e., approximately 10% to 40% of total calories)
Increases tumor incidence in various tissues; conversely, animals con-
suming low fat diets have a lower tumor incidence. When the intake of
1-5
total fat Is low, polyunsaturated fats appear to be more effective than
saturated fats In enhancing tumorigenesis. However, this distinction
becomes less prominent as total fat Intake Is increased.
Dietary fat appears to have a promoting effect on tumorigenesis.
For example, some studies suggest that the development of colon cancer
is enhanced by the increased secretion of certain bile steroids and bile
acids that accompanies high levels of fat intake. Nonetheless, there is
little or no knowledge concerning the specific mechanisms involved In
tumor promotion. This lack of understanding contributes to our overall
uncertainty about the mechanisms that underlie the effect of diet on
carcinogenesis. Although most of the data suggest that dietary fat has
promoting activity, there is not enough evidence to warrant the complete
exclusion of an effect on initiation.
The committee concluded that of all the dietary components It
studied, the combined epidemiological and experimental evidence Is most
suggestive for a causal relationship between fat intake and the occur-
rence of cancer. Both epidemiological studies and experiments in ani-
mals provide convincing evidence that increasing the intake of total fat
increases the incidence of cancer at certain sites, particularly the
breast and colon, and, conversely, that the risk Is lower with lower
Intakes of fat. Data from studies in animals suggest that when fat
Intake Is low, polyunsaturated fats $re more effective than saturated
fats In enhancing tumorigenesis, whereas the data on humans do not
permit a clear distinction to be made between the effects of different
components of fat. In general, however, the evidence from epidemlolog-
Ic4l and laboratory studies is consistent.
Cholesterol* The relationship between dietary cholesterol and
cancer Is not clear. Many studies of serum cholesterol levels and
cancer mortality In human populations have demonstrated an Inverse
correlation with colon cancer among men, but the evidence is not con-
clusive. Data on cholesterol and cancer risk from studies in animals
are too limited to permit any inferences to be drawn.
Chapter 5 contains a more detailed discussion of these studies.
Protein
The relationship between protein intake and carcinogenesis has been
studied in human populations as well as In the laboratory. These stud-
ies are discussed in Chapter 6.
Results of epidemiological studies have suggested possible associa-
tions between high intake of dietary protein and increased risk for can-
cers at a number of different sites, although the literature on protein
is much more limited than the literature concerning fats and cancer. In
addition, because of the very high correlation between fat and protein
1-6
in the diets of most Western countries, and the more consistent and
often stronger association of these cancers with fat intake, it seems
likely that dietary fat is the more active component. Nevertheless,
the evidence does not completely preclude the existence of an inde-
pendent effect of protein.
In most laboratory experiments, carcinogenesis is suppressed by
diets containing levels of protein at or below the minimum required
for optimal growth. Chemically induced carcinogenesis appears to be
enhanced as protein intake is increased up to 2 or 3 times the normal
requirement; however, higher levels of protein begin to inhibit car-
cinogenesis. There is some evidence to suggest that protein may affect
the initiation phase of carcinogenesis and the subsequent growth and
development of the tumor.
Thus, in the judgment of the committee, evidence from both epidemio-
logical and laboratory studies suggests that high protein intake may be
associated with an increased risk of cancers at certain sites. Because
of the relative paucity of data on protein compared to fat, and the
strong correlation between the intakes of fat and protein in the U.S.
diet, the committee is unable to arrive at a firm conclusion about an
independent effect of protein.
Carbohydrates
As discussed in Chapter 7, information concerning the role of carbo-
hydrates in the development of cancer in humans is extremely limited.
Although some studies suggest that a high Intake of refined sugar or
starch increases the risk of cancer at certain sites, the results are
insufficient to permit any firm conclusions to be drawn.
The data obtained from studies in animals are equally limited,
providing too little evidence to suggest that carbohydrates (possibly
excluding fiber) play a direct role in experimentally induced carcino-
genesis. However, excessive carbohydrate consumption contributes to
caloric excess, and this in turn has been implicated as a modifier of
carcinogenesis.
Dietary Fiber
Considerable effort has been devoted to studying the effects of
dietary fiber and fiber-containing foods (such as certain vegetables,
fruits, and whole grain cereals) on the occurrence of cancer (see
Chapter 8).
Most epidemiological studies on fiber have examined the hypothesis
that high fiber diets protect against colorectal cancer. Results of
correlation and case-control studies of dietary fiber have sometimes
supported and sometimes contradicted this hypothesis. In both types of
1-7
studies, correlations have been based primarily on estimates of fiber
intake obtained by grouping foods according to their fiber content.
In the only case-control study and the only correlation study in which
total fiber consumption was quantified rather than estimated from the
consumption of high fiber foods, no association was found between high
fiber intake and a lower risk of colon cancer. However, the correla-
tion study indicated that the incidence of colon cancer was inversely
related to the intake of one fiber component the pentosan fraction,
which is found in whole wheat products and other food items.
Laboratory experiments also have indicated that the consumption of
some high fiber ingredients (e.g., cellulose and bran) inhibits the in-
duction of colon cancer by certain chemical carcinogens. However, the
results are inconsistent. Moreover, they are difficult to equate with
the results of epidemiological studies because most laboratory investi-
gations have focused on specific fibers or their individual components,
whereas most epidemiological studies have been concerned with fiber-
containing foods whose exact composition has not been determined.
Thus, the committee found no conclusive evidence to indicate that
dietary fiber (such as that present in certain fruits, vegetables,
grains, and cereals) exerts a protective effect against colorectal
cancer in humans. Both epidemiological and laboratory reports suggest
that if there is such an effect, specific components of fiber, rather
than total fiber, are more likely to be responsible.
Vitamins
In recent years, there has been considerable interest in the ,role of
vitamins A, C, and E in the genesis and prevention of cancer. In con-
trast, less attention has been paid to the B vitamins and others such as
vitamin K. Chapter 9 contains more detailed information on the evidence
summarized below.
Vitamin A. A growing accumulation of epidemiological evidence Indi-
cates that there is an inverse relationship between the risk of cancer
and the consumption of foods that contain vitamin A (e.g., liver) or its
precursors (e.g., the carotenoids in green and yellow vegetables). Most
of the data do not show whether the effects are due to carotenoids, to
vitamin A itself, or to some other constituent of these foods. In these
studies, investigators found an inverse association between estimates of
"vitamin A M intake and carcinoma at several sites, e.g., the lung, the
urinary bladder, and the larynx.
Studies in laboratory animals indicate that vitamin A deficiency
generally increases susceptibility to chemically induced neoplasia and
that an increased intake of the vitamin appears to protect against car-
cinogenesis in most, but not all cases. Because high doses of vitamin A
are toxic, many of these studies have been conducted with its synthetic
1-8
analogues (retinoids), which lack some of the toxic effects of the
vitamin. Retinoids have been shown to inhibit chemically induced
neoplasia of the breast, urinary bladder, skin, and lung in animals.
The committee concluded that the laboratory evidence shows that
vitamin A itself and many of the retinoids are able to suppress chemi-
cally induced tumors. The epidemiological evidence is sufficient to
suggest that foods rich in carotenes or vitamin A are associated with
a reduced risk of cancer. The toxicity of vitamin A in doses exceed-
ing those required for optimum nutrition, and the difficulty of epi-
demiological studies to distinguish the effects of carotenes from those
of vitamin A, argue against increasing vitamin A intake by the use of
supplements.
Vitamin C (Ascorbic Acid) . The epidemiological data pertaining
to the effect of vitamin C on the occurrence of cancer are not exten-
sive. Furthermore, they provide mostly indirect evidence since they
are based on the consumption of foods, especially fresh fruits and
vegetables, known to contain high concentrations of the vitamin, rather
than on actual measurements of vitamin C intake. The results of several
case-control studies and a few correlation studies suggest that the con-
sumption of vitamin-C-containing foods is associated with a lower risk
of certain cancers, particularly gastric and esophageal cancer.
In the laboratory, ascorbic acid can inhibit the formation of car-
cinogenic Nhnitroso compounds, both jLn vitro and in vivo. On the other
hand, studies of its inhibitory effect on preformed carcinogens have not
provided conclusive results. In recent studies, the addition of ascor-
bic acid to cells grown in culture prevented the chemically induced
transformation of these cells and, in some cases, caused reversion of
transformed cells.
Thus, the limited evidence suggests that vitamin C can inhibit the
formation of some carcinogens and that the consumption of vitamln-C-
containing foods is associated with a lower risk of cancers of the
stomach and esophagus.
Vitamin E (a-Tocopherol) . Because vitamin E is present in a variety
of commonly consumed foods (particularly vegetable oils, whole grain
cereal products, and eggs), it is difficult to identify population
groups with substantially different levels of intake. Consequently, it
is not surprising that there are no epidemiological reports concerning
vitamin E intake and the risk of cancer.
Vitamin E, like ascorbic acid, inhibits the formation of nitrosa-
mines in vivo and in vitro. However, there are no reports about the
effect of this vitamin on nitrosamine-induced neoplasia. Limited evi-
dence from studies in animals suggests that vitaiaiik I may alsd Inhibit
the induction of tumorigenesis by other chemicals.
1-9
The data are not sufficient to permit any firm conclusion to be
drawn about the effect of vitamin E on cancer in humans.
The B Vitamins, No specific information has been produced by epi-
demiological studies, and there have been only a few inadequate labora-
tory investigations to determine whether there is a relationship between
various B vitamins and the occurrence of cancer. Therefore, no conclu-
sion can be drawn.
Minerals
Of the many minerals present in the diet of humans, the committee
reviewed the evidence for nine that have been suspected of playing a
role in carcinogenesis. The assessment was severely limited by a pau-
city of relevant studies on all but two minerals selenium and iron.
Where data on dietary exposure and carcinogenesis were insufficient,
the committee used information from studies of occupational exposure or
laboratory experiments in which the animals were exposed through routes
other than diet. Chapter 10 contains more detailed information on the
evidence summarized below.
Selenium. Selenium has been studied to determine its role in both
the causation and the prevention of cancer. The epidemiological evi-
dence is derived from a few geographical correlation studies, which have
shown that the risk of cancer is inversely related to estimates of per
capita selenium intake, selenium levels in blood specimens, or selenium
concentrations in water supplies. It is not clear whether this relation-
ship applies to all types of cancer or only to cancer at specific sites
such as the gastrointestinal tract. There have been no case-control or
cohort studies.
Experiments in animals have also demonstrated an antitumorigenic
effect of selenium. But the relevance of these results to cancer in
humans is not apparent since the selenium levels used in most of the
studies far exceeded dietary requirements and often bordered on levels
that are toxic. Earlier reports suggesting that selenium was carcino-
genic in laboratory animals have not been confirmed.
Therefore, both the epidemiological and laboratory studies suggest
that selenium may offer some protection against the risk of cancer.
However > firm conclusions cannot be drawn from the limited evidence.
Increasing the selenium intake to more than 200 yg/day 1 by the use
of supplements has not been shown to confer health benefits exceeding
""The upper limit of the Range of Safe and Adequate Daily Dietary
Intakes published in the Recommended Dietary Allowances (see Chapter
10). .-. .- :.*# .<;*
1-10
those derived from the consumption of a balanced diet. Such supple-
mentation should be considered an experimental procedure requiring
strict medical supervision and is not recommended for use by the public.
Iron. Iron deficiency has been related to an increase in the risk
of Plummer-Vinson syndrome, which is associated with cancer of the upper
alimentary tract. Some evidence suggests that iron deficiency may be
related to gastric cancer, also through an indirect mechanism. Although
epidemiological reports have suggested that inhalation exposures to high
concentrations of iron increase the risk of cancer, there is no evidence
pertaining to the effect of high levels of dietary iron on the risk of
cancer in humans. The limited evidence from animal experiments suggests
that a deficiency of dietary iron may increase susceptibility to some
chemically induced tumors.
The data are not sufficient for a firm conclusion to be drawn about
the role of iron in carcinogenesis.
Copper, Zinc, Molybdenum, and Iodine. Some epidemiological studies
suggest that dietary zinc is associated with an increase in the inci-
dence of cancer at certain sites; others suggest that blood and tissue
levels of zinc in cancer patients are lower, and those of copper are
higher, than in the controls. Results of experiments in animals are
also inconclusive. Different levels of dietary zinc either enhance or
retard tumor growth, depending on the specific test design. High levels
of copper have been observed to protect against chemical induction of
tumors.
There is some epidemiological evidence that a deficiency of molyb-
denum and other trace elements is associated with an increased risk of
esophageal cancer. Limited experiments in animals suggest that dietary
molybdenum supplementation may reduce the incidence of nitrosamine-
induced tumors of the esophagus and forestomach.
Studies conducted in Colombia, Iceland, and Scotland indicated that
iodine deficiency, and also excessive iodine Intake, may increase the
risk of thyroid carcinoma. These observations have not been confirmed
in other countries or in other studies. In general, the results of
studies in animals support the association between iodine deficiency and
thyroid cancer.
The committee concluded that the data concerning dietary exposure to
zinc, copper, molybdenum, and iodine are insufficient and provide no
basis for conclusions about the association of these elements with cancer
risk.
Arsenic, Cadmium, and Lead. Occupational exposure to these elements
is associated with an increased risk of cancer at several sites. Expo-
sure to high concentrations of arsenic in drinking water has been linked
with skin cancer. However, the evidence for cancer risk resulting from
exposure to the normally low levels of these elements in the diet is not
1-11
conclusive* No carcinogenic effects of dietary cadmium and arsenic have
been observed in laboratory experiments, whereas high intakes of certain
lead compounds appear to increase the incidence of cancer in mice and
rats*
On this basis, the committee believes that no firm conclusions can
be drawn about the risk of cancer due to normal dietary exposure to
arsenic, cadmium, and lead.
Inhibitors of Carcinogenesis
Foods and numerous nutritive and nonnutritive components of the
diet have been examined for their potential to protect against carcino-
genesis. In epidemiological studies, investigators have attempted to
correlate the intake of specific foods (and by inference, certain vita-
mins and trace elements) and the Incidence of cancer. In laboratory
experiments, vitamins, trace elements, nonnutritive food additives, and
other organic constituents of foods (e.g., indoles, phenols, flavones,
and isothiocyanates) have been tested for their ability to inhibit
neoplasia (see Chapter 15).
The committee believes that there is sufficient epidemiological
evidence to suggest that consumption of certain vegetables, especially
carotene-rich (I.e., dark green and deep yellow) vegetables and cru-
ciferous vegetables (e.g., cabbage, broccoli, cauliflower, and brussels
sprouts) , is associated with a reduction in the Incidence of cancer at
several sites in humans. A number of nonnutritive and nutritive com-
pounds that are present in these vegetables also inhibit carcinogenesls
In laboratory animals. Investigators have not yet established which,
if any, of these compounds may be responsible for the protective effect
observed in epidemiological studies.
Alcohol
The effects of alcohol consumption on cancer incidence have been
studied in human populations. In some countries, Including the United
States, excessive beer drinking has been associated with an increased
risk of colorectal cancer, especially rectal cancer. This observation
has not been confirmed in other studies. There is limited evidence that
excessive alcohol consumption causes hepatic Injury and cirrhosis, which
in turn may lead to the formation of hepatomas (liver cancer) . When
consumed in large quantities, alcoholic beverages appear to act sytier-
glstically with Inhaled cigarette smoke to increase the risk for cancers
of the mouth, larynx, esophagus, and the respiratory tract. The studies
of alcohol consumption and cancer are discussed in Chapter 11.
1-12
Naturally Occurring Carcinogens
In addition to nutrients, a variety of nonnutritive substances
(e.g., hydrazines) are natural constituents of foods. Furthermore,
metabolites of molds (e.g., mycotoxins such as the potent carcinogen
aflatoxin) and of bacteria *(e.g* , carcinogenic nitrosamlnes) may con-
taminate foods. Many of these are occasional contaminants, whereas
others are normal components of relatively common foods. In Chapter
12, the committee examines evidence linking consumption of some of
these substances to carcinogenesis.
The committee concluded that certain naturally occurring contami-
nants in food are carcinogenic in animals and pose a potential risk of
cancer to humans. Noteworthy among these are mycotoxins (especially
aflatoxin) and N-nitroso compounds, for which there is some epidemic-
logical evidence. Studies in animals indicate that a few nonnutritive
constituents of some foods, such as hydrazines in mushrooms, are also
carcinogenic.
The compounds thus far shown to be carcinogenic in animals have
been reported to occur in the average U.S. diet in small amounts; how-
ever, there is no evidence that any of these substances individually
makes a major contribution to the total risk of cancer in the United
States. This lack of sufficient data should not be interpreted as an
indication that these or other compounds subsequently found to be car-
cinogenic do not present a hazard.
Mutagens in Foods
Mutagens are substances that cause heritable changes in th6 genet-
ic material of cells. If a chemical is mutagenic to bacteria or other
organisms, it is generally regarded as a suspect carcinogen, although
carcinogenicity must be confirmed in long-term tests in whole animals.
As is evident from the discussion in Chapter 13, considerable
attention has recently been directed toward mutagenic activity in
foods. Many vegetables contain mutagenic flavonoids such as quercetin,
kaempferol, and their glycosides. Furthermore, some substances found
in foods can enhance or inhibit the mutagenic activity of other com-
pounds. Mutagens in charred meat and fish are produced during the
pyrolysis of proteins that occurs when foods are cooked at very high
temperatures. Mutagens can also be produced during normal cooking of
meat at lower temperatures. Smoking of foods as well as charcoal
broiling results in the deposition of mutagenie and carcinogenic poly-
nuclear organic compounds such as benzofajpyrene on the surfiae^ of the
food. "~
Most mutagens detected in foods have not been adequately tested for
their carcinogenic activity. Thus, the committee believes that it is
not yet possible to assess whether such mutagens are likely to contrib-
ute significantly to the incidence of cancer in the United States.
1-13
Food Additives
In the United States, nearly 3,000 substances are intentionally
added to foods during processing. Another estimated 12,000 chemi-
cals (e.g., vinyl chloride and acrylonitrile, which are used in food-
packaging materials) are classified as indirect (or unintentional)
additives, and are occasionally detected in some foods. Large amounts
of some additives, such as sugar, are consumed by the general popula-
tion, but the annual per capita exposure to most indirect additives
represents only a minute portion of the diet. Although the Food Safety
Provisions and, in many cases, the "Delaney Clause" of the Federal Food,
Drug, and Cosmetic Act^ prohibit the addition of known carcinogens
to foods, only a small proportion of the substances added to foods
have been tested for carcinogenicity according to protocols that are
considered acceptable by current standards. Moreover, except for the
studies on nonnutritlve sweeteners, only a few epidemiological studies
have been conducted to assess the effect of food additives on cancer
incidence.
Chapter 14 contains detailed information on certain additives,
i.e., selected nonnutritive sweeteners, antioxidants, and additives
used in packaging or for promoting the growth of animals used for
food. Particular attention is given to substances to which humans
are widely exposed.
Of the few direct food additives that have been tested and found
to be carcinogenic in animals, all except saccharin have been banned
from use in the food supply. Only minute residues of a few indirect
additives that are known either to produce cancer in animals (e.g.,
acrylonitrile) or to be carcinogenic in humans (e.g., vinyl chloride
and diethylstilbestrol) are occasionally detected in foods.
The evidence reviewed by the committee does not suggest that the
increasing use of food additives has contributed significantly to the
overall risk of cancer for humans. However, this lack of detectable
effect may be due to their lack of carcinogenicity, to the relatively
recent use of many of these substances, or to the Inability of epide-
miological techniques to detect the effects of additives against the
background of common cancers from other causes.
Environmental Contaminants
Very low level? of a large and chemically diverse group of environ-
mental contaminants may be present in a variety of foods. The dietary
levels of some of these substances are monitored by the Market Basket
Surveys conducted by the F6od and Drug Administration. Many of them
have been extensively tested for carcinogenicity.
2 Sec. 402(a)(2)(C) and Sec. 409(c)(l)(A) , respectively.
1-14
In Chapter 14, the committee has summarized the evidence concern-
ing exposure of humans to, and the carcinogenicity of, selected pesti-
cides, some industrial chemicals, and other environmental contaminants.
As with food additives, consideration was given primarily to compounds
to which humans are widely exposed.
The results of standard chronic toxicity tests indicate that a num-
ber of environmental contaminants (e.g., some organochlorine pesticides,
polychlorinated biphenyls, and polycyclic aromatic hydrocarbons) cause
cancer in laboratory animals. The committee found no epidemiological
evidence to suggest that these compounds individually make a major con-
tribution to the risk of cancer in humans. However, the possibility
that they may act synergistically and may thereby create a greater car-
cinogenic risk cannot be excluded.
Contribution of Diet to Overall Risk of Cancer
By some estimates, as much as 90% of all cancer in humans has
been attributed to various environmental factors, including diet (see
Chapter 18). Other investigators have estimated that diet is respon-
sible for 30% to 40% of cancers in men and 60% of cancers in women.
Recently, two epidemiologists suggested that a significant proportion
of the deaths from cancer could be prevented by dietary means and that
dietary modifications would have the greatest effect on the incidence
of cancers of the stomach and large bowel and, to a lesser extent, on
cancers of the breast, the endometrium, and the lung.
The evidence reviewed by the committee suggests that cancers of
most major sites are influenced by dietary patterns. However, the
committee concluded that the data are not sufficient to quantitate the
contribution of diet to the overall cancer risk or to determine the
percent reduction in risk that might be achieved by dietary modifica-
tions.
INTERIM DIETARY GUIDELINES
It is not now possible, and may never be possible, to specify a diet
that would protect everyone against all forms of cancer. Nevertheless,
the committee believes that it is possible on the basis of current evi-
dence to formulate interim dietary guidelines that are both consistent
with good nutritional practices and likely to reduce the risk of cancer.
These guidelines are meant to be applied in their entirety to obtain
maximal benefit.
1. There is sufficient evidence that high fat consumption is linked
to increased incidence of certain common cancers (notably breast and
colon cancer) and that low fat intake is associated with a lower inci-
dence of these cancers. The committee recommend* that the consumption
1-15
of both saturated and unsaturated fats be reduced in the average U.S.
diet. An appropriate and practical target is to reduce the intake of
fat from its present level (approximately 40%) to 30% of total calo-
ries in the diet. The scientific data do not provide a strong basis
for establishing fat intake at precisely 30% of total calories. Indeed,
the data could be used to justify an even greater reduction. However,
in the judgment of the committee, the suggested reduction (i.e., one-
quarter of the fat intake) is a moderate and practical target, and is
likely to be beneficial.
2. The committee emphasizes the importance of including fruits,
vegetables, and whole grain cereal products in the dally diet. In
epidemiological studies, frequent consumption of these foods has been
inversely correlated with the incidence of various cancers. Results
of laboratory experiments have supported these findings in tests of
individual nutritive and nonnutritive constituents of fruits (especially
citrus fruits) and vegetables (especially carotene-rich and cruciferous
vegetables).
These recommendations apply only to foods as sources of nutrients
not to dietary supplements of individual nutrients. The vast litera-
ture examined in this report focuses on the relationship between the
consumption of foods and the incidence of cancer in human populations.
In contrast, there is very little information on the effects of various
levels of individual nutrients on the risk of cancer in humans. There-
fore, the committee is unable to predict the health effects of high and
potentially toxic doses of isolated nutrients consumed in the form of
supplements.
3. In some parts of the world, especially China, Japan, and Ice-
land, populations that frequently consume salt-cured (including salt-
pickled) or smoked foods have a greater incidence of cancers at some
sites, especially the esophagus and the stomach. In addition, some
methods of smoking and pickling foods seem to produce higher levels of
polycyclic aromatic hydrocarbons and N-nitroso compounds. These com-
pounds cause mutations in bacteria ancf cancer in animals, and are sus-
pected of being carcinogenic in humans. Therefore, the committee recom-
mends that the consumption of food preserved by salt-curing (including
salt-pickling) or smoking be minimized.
4. Certain nonnutritive constituents of foods, whether naturally
occurring or Introduced Inadvertently (as contaminants) during pro-
duction, processing, and storage, pose a potential risk of cancer to
humans. The committee recommends that efforts continue to be made to
minimize contamination of foods with carcinogens from any source. Where
such contaminants are unavoidable, permissible levels should continue to
be established and the food supply monitored to assure that such levels
are not exceeded. Furthermore, intentional additives (direct and indi-
rect) should continue. to be evaluated for carcinogenic activity before
they are approved for use in the food supply.
1-16
5. The committee suggests that further efforts be made to identify
mutagens in food and to expedite testing for their carcinogenicity.
Where feasible and prudent, mutagens should be removed or their con-
centration minimized when this can be accomplished without jeopardizing
the nutritive value of foods or introducing other potentially hazard-
ous substances into the diet.
6. Excessive consumption of alcoholic beverages, particularly com-
bined with cigarette smoking, has been associated with an increased risk
of cancer of the upper gastrointestinal and respiratory tracts. Consump-
tion of alcohol is also associated with other adverse health effects.
Thus, the committee recommends that if alcoholic beverages are consumed,
it be done in moderation.
* * *
The committee suggests that agencies involved in education and pub-
lic information should be encouraged to disseminate information on the
relationship between dietary and nutritional factors and the Incidence
of cancer, and to publicize the conclusions and interim dietary guide-
lines in this report. It should be made clear that the weight of evi-
dence suggests that what we eat during our lifetime strongly influences
the probability of developing certain kinds of cancer but that It Is not
now possible, and may never be possible, to specify a diet that protects
all people against all forms of cancer. The cooperation of the food
industry should be sought to help implement the dietary guidelines de-
scribed above.
Since the current data base is Incomplete, future epldemiological
and experimental research is likely to provide new insights into the
relationship between diet and cancer. Therefore, the committee suggests
that the National Cancer Institute establish mechanisms to review these
dietary guidelines at least every 5 years.
CHAPTER 2
CANCER: ITS NATURE AND RELATIONSHIP TO DIET
Before discussing the effects of diet and nutrition on the incidence
of cancer, it is useful to review what is known about the nature of can-
cer, the basis for suspecting a relationship between diet and cancer, and
the stages of carcinogenesis at which diet may exert an effect.
The following review is meant for a general audience. To avoid being
too long, it oversimplifies several issues. For a more complete cover-
age, the reader should turn to two books Origins of Human Cancer (Hiatt
et^aJL., 1977) and Cancer ; Science and Society (Cairns, 1978) and a
journal article entitled "The causes of cancer: Quantitative estimates
of avoidable risks of cancer in the United States today 11 (Doll and Peto,
1981).
THE NATURE OF CANCER
Cancers are populations of cells in the body that have acquired the
ability to multiply and spread without the normal restraints. To under-
stand how such populations arise and the nature of their abnormality, It
is necessary to understand how cells normally control their own behavior.
This subject falls within a branch of basic biology that is still not
well understood.
The Control of Cell Division During the Growth and Replacement of Normal
Tissues
The adult human body contains about ten trillion (10*3) cells. Some
of these cells (e.g., the neurons and striated muscle cells) are incapable
of undergoing cell division; some (e.g., the cells of the marrow and the
epithelial cells of the gut and skin) are actively dividing throughout our
adult life; and others (e.g., the cells of the liver) retain the ability
to divide, but multiply rapidly only when tissues are undergoing regenera-
tion after having been damaged. During our entire adult life, the gross
and microscopic anatomy of the body is preserved by precise systems that
regulate cell division. Cancer develops from cells that escape such
regulation*
Although developmental biologists have for many years studied the
operation of these regulatory systems, few of the signals that control
cell behavior in multicellular animals have been identified. Certain,
tissues (e.g., the endocrine glands, the liver, and the bone marrow)
serve general (systemic) functions rather than local functions; their
role Is to add or subs tract substances or cells from blood. The extent
2-2
of cell multiplication in such tissues must be under general control
and therefore must be regulated by various hormones circulating in the
blood. Many of these hormones have been identified, and the general
features of their operation, if not the precise molecular mechanism,
are now well understood. By contrast, local signals that influence each
cell's reaction to its immediate environment have not been identified.
Yet, these are the signals that are responsible for the microscopic
architecture of each tissue. As the result of numerous experiments on
tissue development and regeneration, we know that local signals pass
between cells, but we still do not know much about their nature.
The entire network of signals serves to maintain the stability and
integrity of each organ and tissue, and to protect the organism from any
form of uncontrolled growth. For the organism as a whole, the forces of
natural selection are inexorably at work: animals that multiply fastest
win the race for survival. Within each multicellular organism, however,
natural selection must be held at bay. Fortunately, the controls work
very well. Although some 10^ cell divisions occur within each human
being during his or her lifetime, only about one-third of the U.S. popu-
lation will develop a clinically detectable cancer.
Various Abnormalities of Cell Behavior
Until the signalling systems that impose territoriality upon the
cells of the body are better understood, it is going to be difficult to
determine the way a cell must be altered to free it from these restraints
and allow it to form a tumor. During the early days of cancer research,
many people hoped that all cancer cells would prove to be defective in
one particular, common feature (e.g., in their ability to respond to a
specific restraining signal received by all tissues), but this now seems
most unlikely. The different forms of uncontrolled growth that lead to
the different varieties of benign and malignant (cancerous) tumors appear
to have distinct causes.
The adult human body contains several hundred different classes of
cell that can be distinguished by their morphology, their relationship
to other cells, the chemistry of their products, and their response to
various hormones and to changes in their environment. Cells in each of
these classes are capable of uncontrolled growth and tumor formation,
but cells in some classes seem more at risk than others. For example,
cancers derived from nerve cells are confined almost entirely to young
children, probably because neurons lose their ability to multiply when
embryogenesis is complete. In humans of all ages, cancers are common in
the epithelial cells of the gut and skin, perhaps because these cells are
continually undergoing division and replacement throughout life. The
epithelial cells in the breast seem to be particularly susceptible to
certain ill-defined carcinogenic factors during the interval between
onset of menstruation and the first pregnancy. In all, several hundred
forms of uncontrolled growth are now recognized and, as the result of
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some 100 years of clinical study involving a vast number of patients,
the usual behavior of each of these kinds of tumor is now well estab-
lished .
The range of cell behavior is very great. At one extreme there
are such trivial abnormalities as the localized growth of melanocytes,
which creates the common freckle. (Indeed, In fair-skinned people who
are frequently exposed to sunlight, freckles are regarded as a normal
abnormality.) At the other extreme is malignant melanoma, a cancer
arising from skin melanocytes. This form of cancer Is often rapidly
fatal because it has a marked tendency to undergo swift dissemination
through the bloodstream to all organs of the body. Between these ex-
tremes, all levels of severity can be found. Many tumors vary little
in their behavior from one patient to the next. For example, the com-
monest tumor of the uterus (the benign fibroma or lelomyoma) arises in
the smooth muscle of the uterus and can grow to enormous size, but the
cells of the tumor virtually never invade the surrounding tissue or
spread to distant sites. Similarly, the commonest tumor of the facial
skin (the basal cell carcinoma) is locally very Invasive, but It also
never spreads to distant sites. Other tumors, such as those in the
breast, are much less predictable; some of them spread quickly and
others do not.
The pathological classification of all these growth abnormalities
(or neoplasias) depends on (1) the tissue of origin, (2) the type of cell
involved, and (3) most importantly, whether the abnormal cells are con-
fined to their original location (In which case the tumor Is classified
as benign) or have invaded the surrounding tissues or "metastasized" to
distant sites (In which case the tumor counts as a cancer). Cancers that
arise in the epithelial cells are called carcinomas, and they account for
more than 90% of all human deaths from cancer. Cancers that arise in the
progenitors of the circulating cells of the blood are called leukemlas
(If the abnormal cells are circulating) and lymphomas or myelomas (If the
cancer affects lymphocytes that tend to be localized In the lymph nodes
or the bone marrow, respectively) * Cancers that arise in fibrous con-
nective tissue or bone are called sarcomas t Together these nonepithelial
cancers account for slightly less than 10% of deaths from cancer. The
pathological classification goes further and subdivides the carcinomas
according to the tissue of origin (e.g., hepatocarclnoma) or the behavior
of the component cells (e.g., adenocarcinoma and squamous cell carcinoma).
Cancer and Cell Heredity
It seems likely that most cancers arise from the proliferation of
a single altered cellt Every tissue of the body has been shown to be
made up of a very large number of small hereditarily similar nests (fam-
ilies) of cells. Therefore, any large piece of tissue will contain
cells that are members of several of these families (I*e. , they come
from different branches of the family tree of cells descended from
original fertilized egg). Cancers, however, prove almost without
2-4
exception to contain cells from only one family (i.e., they must have
arisen within a single family) a finding that is most easily explained
by assuming that each cancer is descended from a single abnormal cell.
However, it is also clear that even though cancers are in this sense
clonal, a considerable amount of modification by variation and natural
selection can occur during the growth of each cancer. For example,
although a particular cancer may be marked, from the start, with a
particular chromosomal abnormality, further abnormalities may be added
during its subsequent growth. It is as if an early step had permitted
uncontrolled growth and the operation of natural selection, which in
turn allowed the progressive evolution of increasingly abnormal and more
rapidly multiplying types of cells. Because the average cancerous growth
will amount to many millions of cells before it becomes detectable, it
may already have undergone considerable selection for the fittest vari-
ants arising spontaneously within the population. So, even if two sep-
arate cancers were to start off with the same underlying abnormality,
they could have very different characteristics by the time the diagnosis
of cancer becomes possible. This makes it very difficult to be certain
whether the great diversity of phenotypic characteristics observed in
most forms of cancer means that there has to be great diversity in the
ways of producing cancer.
The Varying Incidence of Cancer
It is abundantly clear that the incidence of all the common cancers
in humans is being determined by various potentially controllable exter-
nal factors, because people in different parts of the world suffer from
different kinds of cancer, depending on their habits, diet, and customs
rather than on their ethnic origins. Thus, when people migrate from one
country to another they tend to acquire the pattern of cancer that is
characteristic of their new home. This is surely the most comforting
fact to come out of all cancer research, for it means that cancer is, in
large part, a preventable disease.
Next, it is also clear that some carcinogens tend to be associated
with specific cancers. For example, cigarette smoke is the major cause
of the common bronchogenic carcinoma of the lung, but it does not cause
the less common mesothelioma of the lung. Asbestos causes both meso-
theliomas and bronchogenic carcinomas. Certain aniline dyes (especially
2-naphthylamine) cause bladder cancer, but little of any other kind of
cancer. A similar specificity probably also applies to cancers whose
cause or causes have not yet been identified, because the incidences of
the different kinds of cancer tend to vary independently.
Although the causes of most cancers that are common in affluent in-
dustrialized nations have not yet been identified, epidemiological data
suggest certain general conclusions about the nature of these causes.
Apart from lung cancer (which has become much more prevalent during this
century as more and more people have taken up smoking), the only common
2-5
cancers to have changed much in Incidence during the 20th century are
stomach and uterine cancers, both of which have become much less common.
So it seems probable that most cases of the cancers that are common today
are not being caused by the products of modern industry. In fact, the
same conclusion can be reached In quite a different way, because the
incidence and age-specific death rate from many of the common nonrespi-
ratory cancers has been found to be higher in certain nonindustrialized
nations like New Zealand than in the United States. It seems likely,
therefore, that the common cancers not attributable to smoking are re-
lated, for the most part, not to industrialization but to various other
long-standing features of our lifestyle, especially diet.
Experimentally Induced Carcinogenesis
Before considering how Ingredients of the diet (or any other factor
that varies from one population to another) could determine the inci-
dence of cancer, it would be helpful if we had more information about
the kinds of event that can turn a normal cell into a cancer cell. In
principle, this information can come from experimental studies of car-
cinogenesis.
Much of this report is concerned with certain experimental systems
for producing (or preventing) cancer in animals. These experiments show
that a variety of treatments and agents affect the incidence of cancer.
If only one general class of agent or treatment had proved to be carcino-
genic, it would then have been clear what kinds of substance we should,
if possible, be trying to eradicate from our lifestyle or environment.
In fact, a bewildering array of agents and treatments have been shown to
influence the incidence of cancer in animals.
The most widely studied method for producing cancer Is to expose an
animal to repeated doses of any physical or chemical agetit that damages
DNA and causes mutations. In certain instances it has been possible to
show that the cancers produced by these agents are Indeed arising as the
consequence of damage to DNA. This has led people to postulate that the
substances that are the important determinants of cancer In humans will,
for the most part, prove to be agents that produce mutations. The idea
Is attractive because the cancer cell plainly has a defect that can be
Inherited by all Its descendants. Moreover, several quick and inexpen-
sive methods have been developed for detecting mutagens im our environ-
ment. However, it is clear that .many, perhaps most, examples of carcin-
ogenesis In laboratory animals actually proceed by way of a sequence
of steps, some of wblch are brought about by the nmtageus, whereas other,
later steps are driven by agents (promoters) that are not mtitagenlc.
One of the most fully studied examples of "multistep" carcinogenesis
is the induction of skin cancer in mice. The first step, referred to as
Initiation, can be produced by any of a wide range of mutagens. The step
appears to occur rapidly and to be essentially irreversible and Is assumed
2-6
to be a direct consequence of damage to the DNA of those cells in the
skin that normally proliferate and differentiate to produce the scaly
cells that protect the body surface. To complete the process, it is
then necessary to expose the skin for a prolonged period to various
promoting agents that modify or accelerate the normal process of cell
turnover. Because initiation is essentially irreversible, the process
^ promotion will produce cancer, even if a long time is allowed to
elapse between initiation and promotion.
The nature of the events taking place during these later stages of
carcinogenesis is still very obscure. For example, it is not simply a
matter of forcing the initiated cell to divide quickly, because certain
agents that provoke cell proliferation do not act as promoters. Most
promoting agents (e.g., the irritant phorbol esters in croton oil) have
a wide range of effects on the physiological functions of cells, espe-
cially on reactions taking place in the cell membrane. But there is no
reason to believe that they have any direct action on DNA. Unlike in-
itiation, the steps driven by promoters must be to some extent rever-
sible because the effects of prolonged exposure to a promoter such as
croton oil are lost if too long an interval is allowed between each
application. To complicate matters still further, there is good evi-
dence that promotion can itself be divided into two classes of events,
each of which can be driven and inhibited by specific agents. So far,
however, the exact molecular biology of these later events in carcino-
genesis remains obscure.
The predominant effects of the mutagens commonly used in experiments
in animals are localized changes in DNA, usually affecting only one or
two base pairs. There are, however, other ways to Induce cancer in ani-
mals that do not involve local changes in base pair sequence. For exam-
ple, approximately one-quarter of all viruses known to infect vertebrates
are capable of causing cancer in some animal or other. Many of these
viruses probably are carcinogenic because they lead to novel juxtaposi-
tions of genes from the virus and the host. Perhaps for this reason they
tend to cause particular kinds of cancer (e.g., lymphomas, leukemias, or
sarcomas) rather than act as general nonspecific carcinogens. Certainly,
there is little evidence that they are acting as mutagens.
Certain cancers can be produced simply by transplanting cells to
novel sites in the body where they can multiply without the usual re-
straint or by placing them next to inert solid surfaces such as plas-
tic or metal. It seems unlikely that mutation plays any part in these
processes, especially since certain of the cancers produced in this way
will recover their normal restrained behavior when they are returned to
their normal location.
One conspicuous (and neglected) group of cancers results from over-
feeding a treatment that is obviously not mutagenic. The incidence of
these cancers can be reduced by reductions in food intake. These effects
2-7
of nutrition on the incidence of several kinds of "spontaneous" cancer
in animals are very much like some of the correlations between diet and
cancer that have been observed by epidemiologists correlations that
involve most of the major forms of cancer.
Laboratory studies of carcinogenesis are therefore offering us a
choice of possible mechanisms for the formation of the major cancers in
humans. There appears to be no way of guessing which are likely to be
the important mechanisms of carcinogenesis in humans until further epi-
demiological studies have been conducted to isolate and identify the
variables that determine cancer rates in humans.
THE CAUSES OF CANCER
The commonest cancer in Western nations is lung cancer. Its inci-
dence is related to each nation's consumption of cigarettes not to
its level of industrialization. Thus, it is safe to be a nonsmoker in
the United States, but it is not safe to be a smoker anywhere, even in
the clean air of a country like Finland. A somewhat similar observation
has been made for the next two most common cancers: cancer of the large
intestine and breast. Both of these cancers are associated in some way
with long-standing affluence, but they are apparently not linked to in-
dustrialization. Thus, the incidence of both cancers in an industrialized
country like Czechoslovakia is not nearly as high as it is in New Zealand,
which has one of the highest rates for both cancers despite its lack of
the oil and coal required for chemical and manufacturing industries and
its dependence on dairy and agricultural products for income.
The incidence of the other major cancers also varies greatly from
one nation to the next, but not in the way most of us must have been led
to believe from reading the many news reports about newly discovered car-
cinogens in our environment. Apart from cigarettes, the causes of most
of today's cancers do not bear any simple and direct relationship to the
intended and unintended products of industry and to what might be called
the more unnatural features of modern life. This is not to say that in-
dustrial exposure is harmless, but simply that relatively few of the
middle-aged and older members of our current population have been exposed
to great occupational hazards* For those who were exposed, the hazards
are real and inexcusable. In addition, we have to remember that the time
course of carcinogenesis commonly extends over 20 years or more. This
means that we have to be ^ery concerned about the possible long-term
effects resulting from exposure to novel hazards.
Investigation of the Causes of aancer has been an important branch
of cancer research. Early in the course of such studies it became
apparent that genetic factors were not responsible for international
differences in cancer incidence. When groups of people migrate from one
country to another, thereby changing their environment and way of life,
2-8
they tend to leave behind the cancers typical of their homeland and ac-
quire those of their new country. It is almost as if they are offering
us the results of a calculated experiment; indeed, to make the experiment
more perfect, several migrant groups have tended to intermarry for sev-
eral generations rather than to outbreed with the other inhabitants of
their new country. Although studies of migrants have some drawbacks,
they have made an invaluable contribution to research on cancer in humans.
For example, the fact that blacks and Japanese within the United States
develop the spectrum of cancers that is generally typical for the U.S.
population but different from that in Africa and Japan tells us that most
cancers must have external causes and, in principle, should therefore be
preventable.
Certain causes of cancer have been fairly obvious for a long time.
For example, it was not difficult to connect sunlight with skin cancer.
Similarly, it seemed likely that the ever-increasing number of lung
cancers would prove to be related to something that people were breath-
ing. For most cancers, however, likely candidates for the causes were
not immediately apparent.
The list of forces that play upon us, and are likely to change if
we move from one country to another, is not impossibly long. Such
forces obviously include the air we breathe, the water we drink, and
the food we eat, as well as the way we prepare the food and apportion
it into meals. The list should include the infectious diseases that
we contract and perhaps, in a more general sense, some measure of our
contact with other living creatures. In addition to the radiation in
sunlight, we are exposed to other forms of radiation that vary somewhat
in intensity from one region to another.
Lifestyles in various countries differ enormously. Cultures vary
in family size, in the age at which reproduction starts, in the stresses
and strains placed on their populations, and in many other ways. Some
of these variables can be precisely measured. For example, it is possi-
ble to estimate accurately the extent to which time spent indoors in cold
climates increases our exposure to the background radiation that emanates
from many building materials, and to speculate that this increased expo-
sure might account for some of the extra incidence of cancer in the north-
eastern United States. Similarly, it is easy to measure exposures to in-
fectious agents. Thus, it was a straightforward exercise to demonstrate
that Burkitt's lymphoma in Africa bears some relationship to a conjunction
of endemic malaria and infection with Epstein-Barr virus. At the opposite
end of the scale, certain other variables are virtually impossible to
quantitate. For example, some people have suggested that stress can cause
cancer, but this hypothesis cannot easily be tested, and there is, as yet,
no reason to think that it is true.
For most of the variables, however, measurements can be made, but
they are not straightforward. Thus, it will require ome care to trace
2-9
all the threads of causality to their source. The cancers are fairly
easy to record, in terms of either incidence or mortality, but the
environmental variables are not. This is especially true for diet.
During the past 200 years, there have been major changes in the nutri-
tional content of our diet and in our exposure and response to infec-
tious diseases. The effects can be seen most readily in migrants. For
example, the children of migrants to the United States are, on average,
taller and live longer than their parents, just as their parents were
taller than their ancestors. Because nutrition has strong effects on
growth, physiology, and longevity, it was natural to suspect that the
effects could extend to cover susceptibility to cancer. This hypothe-
sis has been examined in both epidemiological studies and laboratory
experiments, but the investigation of the association between diet and
cancer is far from complete.
Epidemiologists found it relatively easy to demonstrate a correla-
tion between the diets consumed by modern affluent societies and the
incidence of cancers in such organs as the breast, colon, and uterus.
But it is much more difficult to determine exactly which, if any, of
the dietary components are responsible. For example, certain interested
parties formerly argued that the association between lung cancer and
smoking was not causal; instead, they suggested that the kind of people
who smoke are the kind of people who, for some quite independent reason,
develop lung cancer. This argument had to be resolved by prospective
studies of groups of people who had stopped smoking. Exactly the same
questions now arise about components of our diet: are the associations
causal or coincidental? Unfortunately, it is much harder to find out
what someone is eating than whether or not they smoke. It is important
therefore that we prepare ourselves for a period of uncertainty, be-
tween our present realization that diet affects cancer and our eventual
ability to offer the public a precise formula for minimizing the inci-
dence of cancer.
Although the formula is still not known, we do have some estimate
of the benefits it would bestow. Judging from the observed differ-
ences in cancer rates among populations with different diets, it is
highly likely that the United States will eventually have the option of
adopting a diet that reduces its incidence of cancer by approximately
one-third, and it is absolutely certain that another third could be
prevented by abolishing smoking. Those reductions would be roughly
equivalent to the reduction in mortality from the infectious diseases
brought about by improved hygiene and better health care delivery
during the 19th century.
This .prediction can be made with confidence because soiie majoir
cancers have already been controlled. For example, the mortality due
to stomach cancer in the United States has dropped sharply during the
past 50 years from first to sixth place on the list of most common
cancers a change brought about presumably by some alterations in our
diet that took place during that period.
2-10
What cannot be predicted is the exact way in which we will discover
the precise changes that ought to be made in the nation's diet. As this
report points out several times (especially in Chapter 3), it is not easy
to determine precisely what people are eating now, and it is even more
difficult to learn what they were eating many years ago when the seeds
were presumably being sown for the cancers they now have.
As shown in later chapters, it has been possible to develop in lab-
oratory animals reasonable facsimiles of the common cancers in humans.
By studying these cancers, it may be. possible for the experimentalist to
uncover certain important variables that the epidemiologist would only
discover with difficulty.
THE INFLUENCE OF DIET ON EXPERIMENTALLY INDUCED CANCERS
Most laboratory and domesticated animals have a significant incidence
of cancer during old age. These cancers tend to be affected by changes
in diet in the same way as cancer in their human counterparts. Thus, a
reduction in total intake of food or specific food items tends to lower
the incidence of both "spontaneous" and chemically induced cancer in most
strains of rats and mice. The main exceptions to this rule occur when
some dietary restriction leads to a deficiency disease involving some
particular tissue, thereby raising the incidence of cancer in that tissue.
For example, deficiency of methyl donors such as choline leads to liver
damage and raises the incidence of "spontaneous" liver cancer in rats.
These examples of the influence of diet on experimentally induced
cancers are not easily investigated because the underlying mechanisms and
molecular biology of the cancers are not understood. Indeed, the effects
of diet were often treated as if they were simply a nuisance, being yet
another variable standing between the investigators and their assays for
carcinogenicity .
The Early Stages of Carcinogenesis
As mentioned earlier, the most generally accepted concept of carcin-
ogenesis is that it is a prolonged process that starts when an animal or
human being is exposed to some mutagen (initiator) that can interact
with the DNA. Because chemical initiators have to be reactive to
interact in this way, they are usually unstable and cannot persist very
long in the environment. Thus, a more usual carcinogenic sequence is
exposure to a stable but toxic chemical (e.g., aflatoxin B x ) that has
to be detoxified in an organ such as the liver and, in the process, is
turned into a highly reactive derivative that interacts with the DNA of
the liver cell. In short, most carcinogenic initiators are created
within the body as the result of "metabolic activation." This opens
the way for a number of very complicated effects during carcinogenesis.
2-11
For example, a chemical that is not itself a carcinogen can act as a
cocarcinogen or an anticarcinogen by stimulating or inhibiting one of
the enzymes involved in the metabolism of some carcinogen. An item
in the diet could therefore determine the incidence of cancer not only
because of the carcinogens that it contains but also because of its
various cocarcinogens and anticarcinogens, which can modify the process
of carcinogenesis.
Metabolic activation has one other important consequence. In some
cases, a carcinogen can be partly metabolized in one tissue and then
enter the blood and undergo its final activation in some other, distant
tissue. Therefore, it is not uncommon to observe that a carcinogen fed
to an animal can produce cancer in organs such as breast, brain, lung,
or uterus, which are far from the gastrointestinal tract.
One other variable is also important in determining the course of
initiation. Most cells possess effective methods for repairing DNA.
They are therefore able to undo most of the damage caused by initiating
carcinogens, if there is sufficient time before they have to duplicate
their DNA. It follows that initiators are sometimes made more effective
if administered at the same time as some agent that forces rapid cell
multiplication. For example, the production of liver cancers in choline-
deficient rats, mentioned earlier, proved on further investigation to
result from the action of two separate stimuli an unexpected (and unin-
tended) initiating carcinogen in the diet and the intended deficiency of
choline, which was acting as a cocarcinogen by destroying the liver and
therefore forcing the remaining liver cells to continue regenerating.
Thus, these cancers could have been prevented either by adding choline
to the diet or by removing the carcinogen from the diet*
To summarize, the effect of diet on the initiation of cancer can
be quite complex. The early stages of carcinogenesis can involve the
simultaneous interaction of several independent variables operating in
a variety of ways. But at least this means that the early steps in the
formation of many kinds of cancer may be interceptable in any one of
several ways.
The Late Stages of Carcinogenesis
The late stages of carcinogenesis tend to be even more obscure,
because they involve reactions that are even less well understood than
the biochemistry of metabolic activation, DNA damage, and DNA repair.
For most chemically induced (as opposed to spontaneous) cancers in
laboratory animals, the process of carcinogenesis seems to go through
a succession of stages. The early initiatory steps require exposure to
substances that usually are known to be mutagenic. The later stages are
brought about by agents (promoters) that affect cell differentiation and
provoke cell proliferation. These agents appear to act primarily on pro-
cesses occurring in cell membranes, including the responses to certain
2-12
signalling substances and free radicals. But the molecular biology of
their action remains obscure despite extensive studies on the subject.
This must surely be the outstanding lacuna in experimental cancer re-
search. Many investigators believe that these later stages concern the
gradual expression of all the mutations produced during the early stages,
but several observations do not fit in well with this hypothesis.
Whenever dietary experiments discriminate between the early and late
stages of carcinogenesis, they usually show that the late stages are most
affected by changes in the diet. The mechanisms underlying such effects
are not known, but it is clear that normal dietary components can either
raise or lower the incidence of cancers that have been initiated by expos-
ing animals to carcinogens in the diet or by other routes. The details
of many such experiments are described in the body of this report.
One interesting feature of these experiments is that their results
so closely mimic the human condition. Most laboratory animals fed ad
libitum are grossly obese compared to their wild counterparts. If they
are placed on diets to maintain their weight within the range that would
be found in the wild, their cancer rate tends to drop to very low levels
unless, of course, they are simultaneously exposed to high levels of some
carcinogen. Similarly, obesity has also been associated with higher
rates of cancer at some sites in humans.
In principle, we should be at least as interested in the late stages
of carcinogenesis as in the early stages. Although cancer could in prin-
ciple be prevented by blocking events at any stage, only the young would
receive much benefit if we removed the initiators from our environment,
whereas everyone old and young alike could be benefited by blocking the
late stages. Unfortunately, because the late events of carcinogenesis
are so poorly understood, much more effort has been expended on the study
of initiators. Furthermore, searches for environmental hazards and most
cost-benefit analyses have centered on eradicating the initiators to
which we are exposed, rather than seeking out the promoters.
2-13
REFERENCES
Cairns, J. 1978. Cancer: Science and Society. W. H. Freeman and
Company, San Francisco, Calif. 199 pp.
Doll, R., and R. Peto. 1981. The causes of cancer: Quantitative esti-
mates of avoidable risks of cancer in the United States today. J.
Natl. Cancer Inst. 66:1191-1308.
Hiatt, H. H. , J. D. Watson, and J. A. Winsten, eds. 1977. Origins of
Human Cancer. Cold Spring Harbor Laboratory, Cold Spring Harbor,
N.Y. 3 volumes, 1,889 pp.
CHAPTER 3
METHODOLOGY
As might be judged from the preceding chapter's discussion of the
nature of cancer, It will not be easy to determine what causes cancer*
It Is especially difficult to identify the connections between cancer
and what people eat, not only because of the complex nature of the dis-
ease, but also because of the complex nature of the food supply, the
variations in eating habits, and the limitations of scientific tools.
The classic diet-related disease is associated with a deficiency of
one or more nutrients. The discoveries of the causes and cures of dis-
eases such as scurvy (caused by a lack of ascorbic acid) and beriberi
(caused by a lack of thiamine) led to the development of a specific model
for nutrition research in which nutrient requirements were determined by
producing deficiencies In laboratory animals or volunteers.
The relationships between diet and chronic disease did not emerge
as a major Interest to Investigators until the causes of the princi-
pal deficiency diseases were Identified. Just as it was once difficult
for investigators to recognize that a symptom complex could be caused
by the lack of a nutrient, so until recently has it been difficult for
scientists to recognize that certain pathological conditions might re-
sult from an abundant and apparently normal diet. Adverse effects on
health associated with nutrient excess in humans have long been recog-
nized. Obesity is the most noticeable among them. Other adverse effects
result, at least partly, from the availability (and overuse) of vitamin
and mineral supplements. Certain vitamins and most of the minerals are
known to be toxic above certain levels. But these known adverse (patho-
logic) effects of vitamin and mineral overdoses have, like the deficiency
diseases, a conspicuously direct relationship with the nutrients In ques-
tion. That Is, the effects of denying or restoring a nutrient to an ex-
perimental subject, whether animal or human, are usually observable
within a short time -at most, months. The links between diet and meta-
bolic, degenerative, and malignant diseases are considerably less obvious.
However, because ducti conditions as atherosclerosis or cancer are probably
associated with dietary patterns that extend over a number of years, the
causative agents are difficult to identify.
The possible relationships between diet and cancer have been investi-
gated in studies of human populations and In laboratory experiments using
various in vitro systems (to check substances for their ability to mutate
bacteria~and mutate or transform other cells) or animal models (to test
substances directly for carcinogenicity) . This chapter provides a synop-
sis of the strengths and weaknesses that are inherent In the methods used
3-2
to study these relationships* It also explains the approach adopted by
the committee in evaluating the epidemiological and experimental evidence.
EPIDEMIOLQGICAL METHODS
General Approaches
In epidemiological research on cancer and diet, investigators seek to
associate exposure to dietary risk factors with the occurrence of cancer
in defined population groups. The studies are largely observational, and
may be of several different types:
Descriptive Studies* These studies describe the patterns of disease
occurrence in one or more populations, in components of the same popula-
tion, or in a single population over time. The observed patterns may be
related to certain other environmental variables or characteristics of
the population, such as demographic factors, industrial pollution, or
diet. Data from descriptive studies are suggestive, rather than defini-
tive, and serve primarily to identify population groups at risk and to
generate hypotheses for further investigation.
Correlation Studies. These studies, based on aggregate exposure
data and observed outcomes, provide the next step in establishing mean-
ingful associations. The crudest of these studies are ecological studies
in which national per capita food intake is related to patterns of can-
cer incidence or mortality. This type of analysis is frequently able
to utilize existing data and is a valuable tool for generating new hy-
potheses. At a more refined level, interviews with carefully selected
individuals may be correlated either with group-specific cancer rates or
with regional differences in rates. In such analyses, the data on expo-
sure and those on outcome may be representative of exposure of differ-
ent groups in the population. Consequently, they often do not reflect
true individual associations and thus may be misleading. This is often
referred to as an ecological fallacy.
Case-Control Studies. Unlike descriptive and correlation studies,
case-control studies enable investigators to collect data for individuals
rather than for groups, and they are designed to control for confounding
variables. In these studies, exposure data (such as dietary intake) are
collected for cases with a specific type of cancer and are then compared
with similar exposure data for a suitably selected noncancer group,
usually referred to as "controls" or compeers. Differences iu exposures
between the two groups that cannot be accounted for by chance occurrence
(random errors) or by known biases (systematic errors) represent true
associations between individual exposure and disease and may actually
reflect causal relationships (Ibrahim, 1979; MacMahon and lugh, 1970)*
The strength of the association can be measured by an odds ratio
calculated from a 2 by 2 contingency table.
3-3
Cohort Studies* Similar to case-control studies, cohort studies
focus on individuals and control for confounding variables. Furthermore,
they are less susceptible to bias than case-control studies because the
exposure data are collected prior to the occurrence of the disease. In
the simplest cohort studies, occurrence rates of disease (e.g., cancer)
over time are compared between two groups of individuals with similar
characteristics but with different histories of exposure (e.g., none vs.
any; low vs. high) to the factors being studied. Higher or lower inci-
dence of disease in one group relative to the other implicates the expo-
sure variable as playing a role in the etiology of the disease. Cohort
studies are reported relatively infrequently because the low incidence of
the disease requires following large groups for long periods. This neces-
sitates considerable expenditures of both time and money. Furthermore,
even if a cohort study is prospective, it is limited in that the cohorts
were self-selected and were not randomly assigned as in true clinical
trials or intervention studies. However, dietary intake data from sev-
eral cohort studies of coronary heart disease have enabled investigators
to perform retrospective cohort analyses of diet and cancer (see Chapter
5).
Intervention Studies. In these studies, which are sometimes called
experimental studies, the investigator randomly assigns the subjects to
two (or more) groups, which are then exposed (or not exposed) to differ-
ent levels of the substance being studied. Although such studies are
ideal for establishing true causal relationships, opportunities for con-
ducting this type of study are rare. In the past, intervention studies
have most often been undertaken to test the effectiveness of vaccination
programs or new treatments for disease. Their use in future research on
diet and cancer will be discussed in a second report to be prepared by
this committee.
Methods For Determining Dietary Intake
Several standard methods with markedly different levels of precision
are used to determine what people eat. Some of these methods are based
on government production statistics; others use information obtained from
individuals about what they have purchased, prepared, or eaten.
Group Dietary Data. Comparisons of diets for different population
groups are generally based on one or two types of data: national per
capita fobd intakes (also called food disappearance data) or house-
hold food inventories.
Most cross-national studies of cancer incidence comparing national
per capita "intake" of various foods or nutrients are based on figures
derived from food balance sheets. The intakes are calculated by adding
the total quantity of food |rodu<ied in a country to the quantity of food
imported, and then subtracting the sum of food exported, fed to live-
stock, put to nonfood uses, and lost in storage. These estimates are
3-4
then divided by the total population to yield per capita intakes.
Comparisons of cancer rates at various sites with national per capita
intakes of, for example, fat, fiber, and animal protein are derived from
data such as these. Although national per capita intakes have been very
useful in providing leads for further research, they are inaccurate as
measures of food that has actually been eaten. They really only measure
food that has "disappeared" into the food supply which is why they are
sometimes called "food disappearance data." They do not account for food
produced by individuals, for waste in stores, restaurants, or homes, or
for differences in consumption within a country by different age and sex
groups.
In this report, the term "per capita intake" is used synonymously
with "food disappearance data."
Household food inventories are used in epidemiological studies
to obtain data on the eating patterns of groups of persons who dif-
fer geographically, socioeconomically, ethnically, or in other ways.
Food intake over a fixed period, usually 1 week, is estimated either
by trained workers who visit individual homes or by the person in the
household responsible for food preparation who is asked either to re-
cord purchases and menus or to recall household food use. Average per
capita intakes of food and nutrients are calculated by dividing the
total household intake by the number of persons in the family. A major
limitation of this method is that it assumes uniform food distribution
for members of the individual household.
Individual Dietary Data. Of necessity, individual food consumption
data must be provided by individual assessments usually reports from
the subjects themselves, but occasionally reports from family members
who share their living quarters. Such information is obtained from three
basic sources: recent (e.g., 24-hour) recall, food records, or diet
history.
The recent recall is used most frequently to measure individual
consumption. In this method, subjects are asked what foods they con-
sumed over a recent specified time usually 1 to 7 days. The 1-day (or
24-hour) recall only requires that each person estimate the amounts of
specific food items consumed during the preceding 24 hours. However,
since the foods consumed may vary considerably from one day to the
next, 24-hour recalls are more reliable as a source of group data than
as a source of individual data, i.e., the average for an entire group
is probably reasonably representative of the eating pattern for that
group. A 24-hour recall may be recorded by the subject or, more often,
by a trained interviewer. He or she may be asked to recall all items
or only certain fdods eaten during the specified period. One sampling
problem is inherent in the 24-hour recall: diets during the weekend may
differ greatly from those consumed during the week. To increase the
representativeness of the 24-hour recall, this method is often combined
with a consumption frequency questionnaire in which subjects are asked
how often they eat selected groups of foods.
3-5
In studies based on food records, participants are asked to main-
tain an accurate diary of all foods consumed during a specified period
(e.g., 1 week). The subjects must estimate the quantity or weigh or
measure each food item eaten at home, allow for inedible portions and
plate waste, and note and measure all ingredients in recipes. They
must also record estimated amounts of foods consumed away from home.
Although the weighed diet record was long viewed as the ideal standard
in estimating dietary intake, it requires, at a minimum, a great deal
of interest and cooperation on the part of the subjects and, hence,
selects for certain types of people. Moreover, this method is likely
to cause subjects to modify their eating patterns to some extent, if
only for purposes of reducing their work load (e.g., by eating fewer
mixed dishes). The accuracy of this method is also compromised in
developed countries, where much of the food eaten is neither prepared
nor consumed in the home. Finally, this method is unsuitable for very
large-scale surveys or studies because of the time and effort involved
in providing detailed instructions to the subjects, in making frequent
follow-up contacts, and in coding the unstructured information from the
records. Despite these limitations, the food record has been used to
validate other methods used for collecting dietary intake data in the
same study population.
Unlike the recent recall, the diet history method does not seek in-
formation on intake during a specified day or week but, rather, attempts
to determine the average pattern of consumption during a particular per-
iod of the subject's life, e.g., just before the onset of an illness.
The intake of selected items or the usual dietary pattern for total in-
take is obtained through interviews or, less often, by self-administered
questionnaire. The information is recorded as frequencies of consumption
or, preferably, as estimated total amounts for the period of study. The
method requires very thorough training of interviewers (or subjects, if
self-administered), careful standardization of the questionnaire, ade-
quate allowances for differences in food preparation, and the provision
of suitable food models to facilitate quantification.
Each of the methods for estimating individual intake has its strengths
and weaknesses, but they share certain limitations. People vary in their
abilities to estimate exactly how much of something they have eaten, and
may sometimes fail to notice (or forget to report) their consumption of
certain foods (e.g., side dishes at meals, peanuts taken from a readily
available supply). Respondents may also know nothing about the ingredi-
ents of the dishes set before them. Furthermore, as mentioned above,
they may alter their eating habits when asked to record their intake. In
case-control studies, there is an additional problem: subjects who are
ill (i.e., cases and sometimes controls) may have altered their diets as
a result of their illness. Although patients are generally asked to re-
call what they ate before the onset of their illness, they may not be
completely successful in this effort.
It is especially difficult to relate diet to a disease like cancer*,
which has a long time course, because we need to learn not only what
3-6
people ate yesterday or during the previous week, but also what they
consumed in the more distant past. (The length of time between expo-
sure and onset of disease depends partly on whether the dietary com-
ponent being studied is an initiator or promoter.) The notion that
subjects can accurately report not only what they usually eat but also
what they usually ate is, for the most part, untested, although limited
data suggest that "recall" of a diet consumed 20 or more years ago may
more closely reflect present food choices than past ones (Garland and
Ibrahim, 1981).
There is considerable potential for variation in the technique used
by interviewers and the introduction of bias during dietary interviews,
especially when very detailed information is required as in studies of
cancer. Depending on the hypothesis being tested, the interviewer may
need to elicit careful descriptions of food preparation methods, of the
fats and oils used for frying, of usual portion sizes, of seasonal vari-
ations in intake, etc. Eliciting such information requires considerable
probing on the part of the interviewer. During this process, subjec-
tivity may be introduced in the recording of responses. For these rea-
sons, researchers active in this field spend considerable time training
interviewers and developing effective instruments and aids (for example,
see Morgan e_t al. , 1978) .
Asking subjects for the same information in two or more different
ways by using several methods in conjunction with one another may also
help to overcome some of these problems. Estimates of quantity can be
improved by using realistic or abstract food models (Morgan et al.,
1978), photographs of graded portion sizes (Hankin et_ al. , 197577 and
similar devices. The strengths and limitations of the major epidemic-
logical methods to study effects of diet have been discussed extensively
in a number of reports (Beaton e al. , 1979; Graham and Mettlin, 1979;
Graham et_ al. , 1967; Hankin e al. , 1975; Marr, 1973; Mettlin and Graham,
1978; Morgan e aJ. , 1978; National Academy of Sciences, 1981; Nichols
t ad., 1976; Nomura e al . , 1976; Reshef and Epstein, 1972).
Biological markers are also used to obtain indirect estimates of
individual intakes. This method has the appeal of objectivity, since it
entails the direct measurement of substances in serum, tissues, or body
wastes as a reflection of actual dietary exposures. Apart from the
difficulty in collecting such data from healthy controls, there are othei
reasons why this method has not been widely used in epidemiological stud-
ies of diet and cancer. Foremost is the difficulty of identifying an
appropriate indicator of past intake. For example, serum levels of some
dietary components, such as cholesterol, do not correlate with informa-
tion on intake and may reflect homeostatic balances or long-term pattern!
of consumption (Pearson, 1967; Underwood e al. , 1970). However, recent
reports on vitamin A serum levels suggest that some such measurements
may nevertheless be useful in predicting cancer risk Jfo cohort studies
(Cambien t al. , 1980; Kark et al. , 1980; Wald ejt al. , 1980) . A particu-
larly troublesome aspect of case-control studies using biological marker!
3-7
(e.g., the relationship of fecal steroids to colon cancer) is that the
markers may themselves reflect consequences rather than antecedents of
the disease.
Analysis of Dietary Data. Regardless of the method used to collect
food intake data, the reported foods must be grouped into categories be-
fore they can be analyzed. Before this can be done, some decision must
be made concerning the kinds of variables that should be compared with
data on the occurrence of cancer. The very first level of decision may
be whether to classify the data in terms of foods or nutrients e.g.,
whether the variable of interest is vitamin C or citrus fruits, carotene
or grams of dark green and deep yellow vegetables. In principle, the
important analytic variables should be identified at the outset of the
study, since that decision will determine the nature and format of the
data that are collected. For example, if the variable of interest is
total calories from fat rather than the characteristics of specific fats,
which may differ according to their sources and processing, then the
interviewer need not help the respondent differentiate between animal
fats and vegetable oils or between liquid and hydrogenated shortenings.
If vitamin C is considered to be the relevant variable rather than fresh
citrus fruit, then no effort need be made to sort out the various forms
in which oranges might be consumed (e.g., as freshly squeezed or frozen
juice, or as whole orange segments). Thus, the nature of the hypothesis
determines the nature of the classification used for data collection.
This explains much of the discrepant data from different investigations
of the same cancer site, although the source of the discrepancy may not
be immediately apparent from even the most careful perusal of the pub-
lished reports.
Since much of the research on the relationship between diet and
cancer has been based on hypotheses regarding the effects of nutrients,
the raw data on foods consumed has most often been translated into nu-
trients, such as grams of protein, animal protein, total fat, satu-
rated and unsaturated fat, cholesterol, and complex carbohydrates. The
quantitative estimates are usually based on food composition tables,
such as those developed by the U.S. Department of Agriculture. (For an
example of these estimates, see Morgan et^ auL . , 1978.) Unfortunately,
the mean values recorded in such sources as USDA Handbook No. 456 (U.S.
Department of Agriculture, 1975) may not reflect the specific composition
of the foods eaten by subjects in a particular study. For example, wide
variations in the nutrient content of unprocessed and processed foods
can result from modifications in processing procedures (e.g., the addi-
tion or removal of nutrients) over time. However, such inaccuracies will
merely tend to weaken any detected association rather than introduce a
spurious association.
Analyses based on individual foods or food groups are not encumbered
by the need to estimate nutrient intake, but are often difficult to in-
terpret because of the multiple comparisons involved. In such analyses,
tlie specific substances responsible for an effect may be difficult to
identify.
3-8
Overall Assessment of Epidemiological Approaches
The major strength of epidemiological studies is that their focus on
human populations circumvents two important limitations of laboratory
research. First, since humans are observed directly, the results do not
have to be extrapolated from one species to another. Second, since the
levels and patterns of exposure studied are those that actually occur
among people, interpolation to low doses from the artificially high ex-
posure levels frequently required in laboratory research can also be
avoided. In addition, since the varieties of human experience produce a
wide range of exposures to a given risk factor, epidemiological investi-
gations are often able to examine directly the effects of different
levels of exposure (i.e., dose-response).
On the other hand, epidemiological studies present some special
difficulties. To begin with, such research is limited by its need to
rely primarily on observational data, because it is difficult and often
unethical to conduct experiments (i.e., intervention studies) on groups
of humans. Furthermore, observational epidemiological studies are open
to errors or bias. For example, persons who agree to participate in such
studies or who are selected as participants by the investigator (e.g.,
hospitalized patients) may not comprise truly representative groups of
subjects and may yield misleading findings.
Unlike studies of cancer among smokers and nonsmokers, dietary stud-
ies are confronted with the inherent difficulty of determining reasonably
precise exposures. For example, the degree to which cases have been
exposed to a particular dietary component may not be sufficiently
different from that of controls to demonstrate any effect. Furthermore,
it is often difficult to determine the specific dietary constituents to
which study participants have been exposed.
Another difficulty inherent in epidemiological studies of diet and
cancer is the long latency period between first exposure and overt man-
ifestation of illness. In case-control studies, this delayed onset makes
it necessary for investigators to learn what the subject ate during some
period beginning long before the study began, or to assume that recent
intakes reflect past exposures. In prospective cohort studies, the in-
vestigator must collect current dietary data and then either wait (for
up to 20 to 30 years) for the disease to appear or identify sufficiently
large groups of subjects for whom there are adequate retrospective
dietary data.
Accuracy in the measurement of both the exposure and the outcome
variables is especially difficult to attain in the studies of diet and
cancer. For example, the frequent dependence on recall data from inter-
viewed subjects virtually guarantees imprecise measurement of dietary
3-9
exposure, which might mask small but real differences between cases and
controls. Correlation studies may suffer from differences among coun-
tries such as completeness of cancer reporting, diagnostic practices, and
terminology. Furthermore, because cancer incidence (occurrence) data are
frequently not available for such studies, reliance must be placed on
mortality data instead. Since mortality reflects survival as well as in-
cidence, it is not an ideal measure for cancer etiology, particularly for
sites where survival rates are high and have notable international vari-
ation. These and other considerations make it especially difficult to
identify subtleties in the relationship between the degree of exposure
and risk of disease.
Most of these deficiencies in epidemiological studies of diet and
cancer are likely to result in nondif ferential misclassif ication, thereby
reducing the likelihood that a given study will be able to demonstrate
true differences that exist between the groups compared. Therefore, the
results of epidemiological studies may often be assumed to represent
conservative estimates of the true risk for cancer associated with the
dietary exposures of interest.
LABORATORY METHODS
As interest in the possible relationship between diet and cancer has
grown in recent years, increasing attention has been paid to the chemical
carcinogens in our diet. The foods that we eat contain a vast number of
separate chemical entities : several thousand as additives and many times
this number as natural constituents. Most of these chemicals are present
in relatively low concentrations, but even small amounts of some potent
carcinogens might be important if they are present in commonly consumed
foods.
There are three major laboratory methods for detecting and identify-
ing chemical carcinogens: analysis of molecular structure, short-term
tests, and long-term bioassays in animals. The first two methods provide
information about potential carcinogenicity, whereas the third provides
direct evidence of carcinogenicity in laboratory animals.
Analysis of Molecular Structure
In a review of the large body of evidence pertaining to the role of
structure-activity relationships in predicting carcinogenic activity,
Miller (1970) suggested that most, if not all, chemical carcinogens are
ultimately electron-deficient reactants (Miller, 1970). Carcinogens have
toeeti identified in more than a dozen chemical classes, which share no
common structural features (Miller and Miller, 1971, 1979). Furthermore,
even within classes, closely related chemicals may differ with respect to
carcinogenicity e.g., 2-acetylaminof luorene (2-AAF) is a well^kiiowB car-
cinogen in several species of animals, whereas its close relative 4-AAF
is not carcinogenic (Office of Technology Assessment, 1981). The major
3-10
utility of the analysis of molecular structure is to screen a variety of
chemicals quickly and to treat the results as warnings rather than as
definitive indicators of carcinogenic activity.
Short -Term Tests
Interest in establishing short-term, relatively quick and inexpensive
procedures for the identification of chemical carcinogens has increased
during the past several years as a result of the realization that the
list of potential chemical carcinogens is growing faster than our capac-
ity to test the materials (Bridges, 1976). Therefore, greater numbers
of potentially hazardous compounds must be screened and placed into a
priority system for further testing. This appears to be the primary role
of short term tests.
Since these tests can be conducted quickly (often in only a day or
two) and inexpensively, they are useful for screening substances for
potential carcinogenicity. For these tests to be useful, they must not
only be faster, easier to interpret, more sensitive, and less expensive
than the standard feeding studies, but they must also be reliable and
relevant to the in vivo assay upon which they are modeled.
A number of validated short-term tests can be used to examine the
capacity of a substance to cause mutations, other genetic alterations,
or neoplastic transformation. These tests can be used with a variety of
biological systems such as bacteria, yeast, mammalian cells, and intact
animals .
To date, the most widely used method appears to be the Salmonella/
microsome assay (also called the Ames test), which utilizes several spe-
cifically constructed Salmonella typhimurium strains to detect various
kinds of mutations and genetic damage (Ames t^ al/ , 1975). It is gen-
erally agreed, but not without considerable controversy, that there is a
high degree of correlation between the mutagenicity of compounds in the
Salmonella /micro some assay and their carcinogenicity in laboratory ani-
mals (McCann and Ames, 1976; Purchase et_ al_ . , 1978; Sugimura e al.,
1976). However, recent studies show that this correlation is~dependent
upon the class of chemical being investigated For most aromatic amines,
polycyclic aromatic hydrocarbons, and direct alkylating agents, there
appears to be a high degree of correlation. On the other hand, chlori-
nated hydrocarbons are difficult to identify as mutagens in the Ames
test, although they are known to be carcinogenic. In vitro mutagenicity
tests have one major drawback: although they may provide a good indica-
tion of whether or not an agent is carcinogenic, they produce very little
information on its relative carcinogenic potency.
Other short-term in vitro and in vivo tests it use include assays
for the induction of DNA damage and repair or 1 ,inutagene&is^ia''vb&cteria,;
in yeast, in Drosophila melanogaster, or in mammalian cells in culture.
Whole mammals can be used in the dominant lethal test, mouse spot test,
3-11
tests for heritable translocations, and tests for chromosome aberrations.
These mammalian mutagenesis bioassays offer promise as prescreening tools
since they seem to provide both qualitative as well as quantitative data,
but they are more expensive to perform and require more time than the
other assays. The n vitro transformation systems are potentially useful
for screening carcinogens, but they are also expensive and time-consuming-
Moreover, the reliability of early markers of oncogenic transformation is
unknown. If the in vitro transformation tests have to be carried out to
the point of injecting presumably transformed cells into a syngeneic ani-
mal to determine if the cells develop into a tumor, then the expense and
time involved are the same or possibly greater than required for some in
vivo carcinogenic! ty test systems.
In general, short-term tests have a number of drawbacks:
Carcinogens or modifiers of carcinogenesis may operate by mecha-
nisms not involving DNA damage and repair. Thus, some agents, e.g.,
tumor promoters, which are particularly relevant when one considers diet,
are not likely to be detected by these tests.
The effects of absorption, transport, activation, detoxification,
and excretion are not taken into account.
Quantitative risk assessment cannot be made easily.
Despite positive results for mutagenicity in a battery of such
tests, many scientists do not accept such evidence alone as an indica-
tion of carcinogenicity. Long-term bioassays in whole animals are still
necessary to make this determination (International Agency for Research
on Cancer, 1980).
Long-Term Bioassays
These tests, which are conducted in animals, have been the most
widely accepted methods for determining the carcinogenic effect of
substances. In the absence of data on humans, all substances demon-
strated to be carcinogenic in animals are regarded as potential car-
cinogens for humans, and the empirical evidence overwhelmingly supports
this hypothesis.
The standard procedure in long-term bioassays is to feed substances
at levels that are just below the maximum tolerated dose for a major
portion of the lifespan of the animal (usually rodents, which have a
life span of 2 to 3 years). The rationale for feeding very high doses of
a substance in chronic bioassays is that the nunber of animals ttiat de^
velop cancer Increases as the dose of the test substance is increased.
To conduct a valid experiment at high doses, only a small number of ani-
mals (a few hundred) is required. An important variable that determines
outcome in these tests is the potency of the carcinogen: the greater
3-12
its potency, the greater will be the number of animals that develop
cancer at a particular dose or increase in the number of tumors per
animal. Alternatively, a carcinogen can decrease the latency period
or the lifespan without altering the tumor incidence. If a chemical
produces cancer in test animals and if the route of administration is
equivalent to the route by which humans are exposed, it is generally
accepted that the compound is potentially carcinogenic in humans.
These bioassays also have some major drawbacks:
An adequately performed feeding study takes several years to
complete and analyze, and costs more than $500,000.
The test lacks sensitivity to detect weak carcinogens. For ex-
ample, if a carcinogen induces cancer in 1% of the test animals, then
an experiment with 50 animals of each sex at each dose will not possess
sufficient statistical power to detect the carcinogenicity of the test
substance.
o False negatives can be obtained because some strains of test ani-
mals are more resistant than others. A negative result means that the
test compound is not carcinogenic for that particular species and strain
under the conditions of the test, but the chemical could be positive in
another species or strain under the same or different conditions.
Extrapolation from the high doses given to animals to predict risk
to humans cannot be accomplished with any degree of confidence, even when
the test compound has been shown to be carcinogenic in a full-scale study
in animals.
Only recently has there been an attempt to standardize tests for
carcinogenicity. Variables include animal species and strain, genetic
characteristics of the test strains, the diet given to the animals, the
chemical and physical characteristics of the test substances, the method
of tissue examination, spontaneous rate of tumor formation in control
animals, susceptibility to various carcinogens, dose response to a given
carcinogen, and tissue specificity of a large number of carcinogens.
Difficulties in Studying the Carcinogenicity and Mutagenicity
of Food Constituents
Because foods contain unidentified chemicals or mixtures of compounds,
it is difficult to test them in long-term bioassays, which require precise
physical and chemical characterization of the test substance. Further-
more, many foods that are not toxic to humans are toxic to laboratory ani-
mals, making it difficult to test these substances at high doses (Elias,
in press).
Because of the mere volume involved, it would be difficult to test
the major components of diets for carcinogenicity by exposing the animals |
3-13
to doses 100 or more times higher than the expected levels of human
exposure. It is also difficult to use different doses because nutrient
imbalance may result from feeding high levels of the dietary component
being tested, and the supplementation of diet with micronutrients to
avoid nutritional deficiencies has not always proved satisfactory.
It is especially difficult to select a valid control diet in these
studies. Ideally, control animals must be fed a diet identical to the
one fed to test animals except that the food or diet being tested should
not contain the presumed carcinogen. If the carcinogen happens to be a
naturally occurring constituent (e.g., aflatoxins), then the carcinogen
will have to be removed from the control diet. However, this generally
leads to many complications such as the introduction of new chemicals
and/or the removal of others in addition to the carcinogen. If the
carcinogen is generated as a result of food processing, then the control
food must be subjected to an alternative type of processing, if possible,
to achieve similar results without generating the carcinogen (Elias, in
press)
Since many dietary carcinogens are probably present in very low
amounts, it would be logical to expose a large number of laboratory
animals to low levels of suspected carcinogens. This may be prohibi-
tively expensive.
Alterations in the diet or nutritional status do not appear to cause
cancer directly in laboratory animals, but are only believed to modify
the spontaneous rate of tumor formation or the induction and growth of
cancer by specific carcinogens. It is important to learn the background
(spontaneous) rate of tumor formation in a given animal model so that
changes induced by altered diets can be evaluated with confidence* It
is also very important to know the dose-response characteristics of car-
cinogens in order to induce a 50% tumor incidence in tests to determine
if a given dietary or nutritional change enhances or inhibits the induced
response. For example, if a carcinogen induces a 90% tumor incidence,
it would be difficult to determine if some change in diet had enhanced
tumorigenesis. Alternatively, it would be difficult to determine if the
dietary changes had a significant inhibitory effect on tumor response if
the carcinogen induced only a low incidence of tumors. Assessment of
risk as related to the time to tumor response is discussed in Chapter 18.
Furthermore, it is important to select the test animal whose response to
the carcinogen being tested most closely approximates the suspected re-
sponse of humans. For example, if a high fat diet appears to be related
to an increased risk for colon and breast cancer in humans, the animal
models selected should be able to develop the same type of tumors.
Many laboratory studies of the effect of diet and nutrition on cat-
cinogenesis have not been well controlled, especially with respect to the
composition of the diets fed to the animals. This is an important con-
sideration because diets are a potential source of naturally occurring
carcinogens and may also contain contaminants with carcinogenic activity.
Diets fed to test animals have ranged from various commercial laboratory
chows to diets so purified that mixtures of individual amino acids are
3-14
fed in place of protein. Specific nutrients may be administered at
levels that range from the marginally deficient to the questionably
excessive. As a consequence, it is difficult to compare results from
these studies. Recent recommendations that standard diets [e.g., the
AIN-76 diet (Anonymous, 1977)] be used should help considerably. Another
drawback is the failure to insure isocaloric intakes by control and
experimental groups. Caloric restriction and total food intake have been
reported to be important determinants of tumor yield (Silverstone and
Tannenbaum, 1949; Tannenbaum, 1944, 1945; Waxier, 1960). The difficulty
in distinguishing between the effects from changes in total food intake
and caloric intake is discussed in Chapter 4. For example, even an
alteration in body size caused by a change in caloric or total food
intake may affect tumor yield (Clayson, 1975). More insight can be
gained by pair-feeding to control for total food intake, nutrient
deficiencies, or weight gain.
n vitro mutagenicity tests were originally developed to assess
the mutagenicity of pure substances, which are much easier to test than
the complex mixtures of compounds contained in foodstuffs. Testing is
especially complicated if the nature and properties of the suspected
substance presumed to be present in the food are not known. Until re-
cently, this problem has been circumvented by using food extracts.
However, this process is subject to numerous criticisms. For example,
active mutagenic substances detected in food extracts may not be present
in the animal during the normal digestive process. On the other hand,
reactions during the digestive process can result in the formation of
mutagens from previously innocuous substances. Furthermore, solvents
used in the extraction procedures could conceivably react with food
constituents, and solvent residues may persist in the extracts re-
sulting in erroneous conclusions (Elias, in press). In vivo mutageni-
city testing of these foodstuffs is comparatively simpler, since the
test substance can be fed to the animals in their diet for several days.
COMMITTEE'S APPROACH TO EVALUATION OF THE LITERATURE
The strengths and weaknesses inherent in the epidemiological and lab-
oratory methods used to study the relationship between diet and cancer
are described above. In the chapters that follow, the committee has re-
frained from presenting a detailed critique of the results and methodology
of each report, because most of the criticisms that apply to individual
studies are in fact limitations imposed by the design of various types of
epidemiological studies, by the method selected to determine dietary in-
take, or by the laboratory tests used, all of which are described in this
chapter. Furthermore, because no studies of this difficult subject are
without limitations, the committee did not wish to place too much empha-
sis on the results, especially the precise quantitative data (e.g., rela-
tive risks in epidemiological studies or tumor incidence im animal ex-
periments), from any single study. Rather, it reviewed all the data and
3-15
based its conclusions on the overall strength of all the evidence com-
bined .
Although the committee considered the evidence from all types of
epidemiological studies, it had the most confidence in data derived from
case-control studies and from the few cohort studies that have been re-
ported. Instead of relying on aggregate correlation data, these studies
are based on the collection and analysis of data on individuals, and in-
vestigators can control for confounding variables. Therefore, the com-
mittee concluded that the evidence on diet and cancer provided by these
two types of studies is more definitive and indicative of meaningful
associations than data derived from correlation and descriptive studies.
Particular emphasis was given to the results of case-control or cohort
studies that were designed to examine a specific hypothesis.
In evaluating laboratory evidence, the committee placed more confi-
dence in data derived from studies on more than one animal species or
test system, on results that have been reproduced in different labora-
tories, and on the few data that indicate a gradient in response.
The preponderance of data and the degree of concordance between the
epidemiological and laboratory evidence determined the strength of the
conclusions in the report.
SUMMARY AND CONCLUSIONS
Both epidemiological studies and laboratory experiments have been
used to examine the relationship between dietary factors and carcino-
genesis. A number of different epidemiological methods have been used.
These include descriptive studies, correlation studies, case-control
studies, and cohort studies. Accurate measurement of intake is funda-
mental to the success of most of these studies. Both food disappearance
data and household food inventories are used to determine the intakes of
groups. Methods used to measure individual nutrient intake are recent
recalls of intake, food records, and diet histories A
The major strength of epidemiological studies is their focus on human
populations. They are the most direct way of investigating the possible
causes of human cancer, thereby avoiding the need to extrapolate data
from animals to humans. Since the exposures studied are those that
actually occur among people, dose-response relationships can be deduced
because different people are exposed to different levels of the variable
under study. Furthermore, interpolation from high doses to low doses,
which would be necessary in the laboratory, is also avoided.
The interpretation of epidemiological studies is complicated by the
heterogeneity of the human population, the wide variety of changing
lifestyles, and difficulties in the accurate measurement of both the
exposure and the outcome variables. Moreover, ethical, social, and
3-16
political considerations preclude manipulating and arranging human affair*
into simpler patterns for analysis. For example, differences among groups
may be difficult to identify if there is little difference in the degree
of exposure to a particular dietary variable. Their interpretation may
be further jeopardized by the lack of specificity of the methods for mea-
suring intake and the uncertainty about whether the data reflect nutrient
intake or whether current intake correlates well with past dietary
patterns (which may be more relevant to carcinogenesis).
Laboratory experimentation on animals is basically an effort to over-
come the limitations of direct studies of cancer in humans. The labora-
tory provides a simplified and controlled environment, and laboratory
animals can be regarded as uniform and controlled populations "standing
in" for human beings. However, the animals are not human, and the eti-
ology of the cancers they develop may not duplicate that for cancers in
humans.
Laboratory tests to study neoplasia are conducted either with whole
animals or with cell cultures in vitro, both of which have limitations.
One general uncertainty lies in projections or extrapolations from lab-
oratory data to humans. On the one hand, the biochemical similarity
among many species means that what happens in one species is likely to
occur in another; on the other hand, some responses may be peculiar to
particular species. An attempted compromise is to assume that if two
nonhuman species react similarly, then humans are likely to have the same
reaction.
Compounds whose carcinogenicity was initially suspected in epidemio-
logical studies can be more quickly and cheaply tested in short-term
laboratory systems than in whole animals. These short-term systems may
involve the use of bacterial cultures, human cells in culture, or even
subcellular mixtures of cell components. Tests on bacteria measure gen-
etic change (mutation) rather than carcinogenesis since the latter has
no direct equivalent in bacteria. Their validity rests on the assump-
tion, backed by considerable data, that carcinogenic substances are
likely to be mutagenic and vice versa. This appears to be true for most
compounds known to be carcinogenic in humans and for many mutagens tested
for carcinogenicity in laboratory animals. However, there are many ex-
ceptions, particularly in establishing quantitative correlations between
mutagenicity and carcinogenicity. Therefore, bacterial tests should be
regarded as useful, especially for screening, but not as an exclusive
method for determining carcinogenicity. Their basic function is the
detection of initiator action not the later stages of tumor promotion
that may be more relevant for dietary factors, since nutrients have
little or no mutagenic activity.
In summary, data obtained in laboratory tests are useful for evalu-
ating the role of dietary and metabolic factors in the development of
cancer in humans. The laboratory experiments tend to be better con-
trolled and more precise than epidemiological investigations. However,
3-17
they are costly in time and money, and they also depend upon simple
assumptions that may not be valid for humans. The projection of such
data to humans must be done cautiously and is most convincing when
accompanied by confirmatory evidence from epidemiological studies.
The two approaches are complimentary and should be used in conjunction
with each other as often as possible.
The committee evaluated the evidence from all types of epidemiologi-
cal studies and laboratory experiments, but had more confidence in data
derived from case-control and cohort studies, in the results of experi-
ments conducted in more than one animal species or test system, in re-
sults that had been reproduced in different laboratories, and in data
that showed a dose response. The preponderence of data and the degree
of concordance between the epidemiological and the laboratory evidence
determined the strength of the conclusions in this report.
3-18
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carcinogens and mutagens with the Salmonella/mammal ian-microsome
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Bridges, B. A. 1976. Short term screening tests for carcinogens.
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Cambien, F., P. Ducimetiere, and J. Richard. 1980. Total serum
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Clayson, D. B. 1975. Nutrition and experimental carcinogenesis : A
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Elias, P. S. In press. Methods for the detection of carcinogens and
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Garland, B., and M. A. Ibrahim. 1981. The reliability of retrospective
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Graham, S., and C. Mettlin. 1979. Diet and colon cancer. Am. J.
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Graham, S., A. M. Lilienfeld, and J. E. Tidings. 1967. Dietary and
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Hankin, J. H., G. G. Rhoads, and G. Glober. 1975. A dietary method
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Ibrahim, M. A., ed. 1979. The case-control study: Consensus and
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International Agency for Research on Cancer. 1980. Long-Term and
Short-Term Screening Assays for Carcinogens: A Critical Appraisal.
IARC Monographs, Supplement 2. International Agency for Research on
Cancer, Lyon, France. 426 pp.
Kark, J. D., A. 1^. Smith, and C. G. Hames. 1980. The relationship
of serum cholesterol to the incidence of cancer in Evans County,
Georgia. J. Chronic Dis. 33:311-322.
MacMahon, B., and T. F. Pugh. 1970. Case-control studies. Pp. 241-
282 in Epidemiology. Principles and Methods. Little, Brown and
Co., Boston, Mass.
Marr, J. W. 1973. Dietary survey methods: Individual and group
aspects. Proc. R. Soc. Med. 66:639-641.
McCann, J. , and B. N. Ames. 1976. Detection of carcinogens as mutagens
in the Salmonella/microsome test: Assay of 300 chemicals: Discus-
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Mettlin, C. J., and S. Graham. 1978. Methodological issues in etio-
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Miller, J. A. 1970. Carcinogenesis by chemicals: An overview
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Liver stores of vitamin A in a normal population dying suddenly or
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23:1037-1042.
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3-21
Research Service, U.S. Department of Agriculture, Washington, B.C.
291 pp.
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J. Clin. Nutr. 8:760-765.
SECTION A
THE RELATIONSHIP BETWEEN NUTRIENTS AND CANCER
The foods comprising the diets of humans are complex mixtures of
chemicals modified by many events that occur between the field and the
table. Only a small proportion of these chemicals have specific nutri-
tional functions. However, much research and, therefore, much of this
report especially the eight chapters that follow are focused on the
relationships between rates of cancer at different sites and consump-
tion of specific nutrients.
This focus is not surprising since diet-related diseases have
characteristically been associated with deficiencies of one or more
nutrients (e.g., scurvy results from a deficiency of vitamin C). The
conquest of such diseases encouraged investigators to look at the
metabolic and degenerative diseases (often called diseases of afflu-
ence) in relation to the same constituents of food consumed in excess.
Yet, as the data reviewed in Chapters 13 and 15 indicate, at least
some of the compounds in food (e.g., flavones, isothiocyanates) that
have been implicated in the causation or prevention of cancer are food
constituents other than nutrients (or additives, o contaminants).
This fact suggests (1) that some food classifications other than the
presently obvious nutrient-based ones may need to be regularly con-
sidered in epldemiological studies and (2) that changes in the chemical
composition of the food supply may need to be monitored and controlled,
even if they do not appear to affect the per capita supply of compounds
classed as nutrients.
CHANGES IN THE FOOD SUPPLY
Table A-l lists the daily per capita intake of nutrients during
certain years between 1909 and 1976. These estimates, based on food
disappearance data reported by Page and Friend (1978), show that if
nutrients alone are measured, the food supply appears to have under-
gone little overall change during this period* There has been a
slight decline in total calories available for consumption, essen-
tially no change in total protein, and a moderate increase in total
fat, balanciiag a similar decline in total carbohydrate. The available
supply of most of the vitamins and minerals measured has remained
essentially unchanged. The exceptions are iron and vitamins B^,
82, and niacin, which have increased, and magnesium, which has de-
creased. The increases probably reflect the enrichment of a variety
of flour-based products. Since magnesium is lost during the refining
of flour, as are a number of trace minerals, the decline in magnesium
intake might reflect a general decline iii trace minerals, especially
those derived from whole grains. If one were Delating U.S. trends
A-2
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In per capita intake to trends in cancer incidence, these data suggest
that the relatively stable nutrient composition of the diet is being
reflected in the relatively stable cancer rates at most sites
However, these figures on the availability of a limited group of
nutrients tend to obscure the extensive changes that have taken place
in the food supply during the past 50 years. Some of these can be seen
by examining the changes that have occurred in the contribution of
various food groups to total calories (Figure A-l). For example, the
percentage of calories derived from grain products has been halved. As
shown in Table A-2, most of this change can be attributed to a decline
in per capita intake of flour: from approximately 131 kg per capita in
1909 to 63 kg in 1976. The intake of fat has also changed in a manner
that is not evident in Table A-l. Although total per capita fat Intake
increased only 27% during this period, fat as a percentage of calories
increased by 35%. There was also a 56% increase in the intake of
separated fats, most of them from vegetable sources. In other words,
as attention shifts from nutrients to food groups and from there to
specific food substances, it becomes increasingly evident that there
have been extensive changes in the composition of what is actually
available to eat.
Meat, poultry, fish
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A-5
There are some data indicating the magnitude of the changes in per
capita intake of certain food items and constituents; however, many of
the changes are not adequately documented. For example, there are no
data on the consumption of whole wheat flour, commercial baby food, or
home-produced vegetables. Moreover, there is no indication whether
fresh vegetables eaten in the Northeast were grown in that region or
whether they were shipped by train from California or by air from
Mexico (Brewster and Jacobson, 1978). A variety of differences in
their chemical composition (e.g., in their vitamin and mineral content)
can result from differences in the way in which these vegetables were
grown, transported, and stored.
Between 1940 and 1977, per capita intake of food color additives
increased tenfold. Soft drink consumption increased 1.5 times in
just 16 years between 1960 and 1976 (Brewster and Jacobson, 1978).
Although total intake of fruits and vegetables increased slightly
between 1909 and 1976 (Table A-2), the intake of fresh fruits and
vegetables 1 actually declined (Table A-3), a major portion of that
decline having occurred after 1948. Changes in the per capita intake
of certain individual commodities are especially striking. For example,
the intake of fresh potatoes is more than two-thirds lower than it was
at the turn of the century and more than one-half lower than it was 30
years ago, whereas the intake of processed potatoes has increased by a
factor of 44 during the same 30 years. The per capita intake of pro-
cessed citrus fruit juice which accounts for much of the increase in
overall fruit intake increased dramatically from an average of less
than one 4-oz (120-ml) serving per person annually in 1948 to 117 4-oz
servings per person in 1976 (Brewster and Jacobson, 1978). Similarly,
the intake of canned or bottled tomato products (e.g., paste, sauce,
catsup, and chili sauce) increased from 2.25 kg per capita in 1920 to
10.1 kg per capita in 1976 (Brewster and Jacobson, 1978). All of these
changes reflect the proliferation of food products on the market from
less than 1,000 at the end of World War II to well over 10,000 at
present (Molitor, 1980).
term "fresh" applied to fruits and vegetables commonly refers to
produce that has been, at most, washed, trimmed, and chilled. The term
"processed" has many meanings; for example, preservation by canning and
freezing, which result in some chemical but little structural change;
extraction and dehydration such as the preparation of orange juice con-
centrate, which produce significant structural and possibly major
chemical changes including nutrient loss; and processes that involve
extensive separation of foods into components, or the fabrication of
new foods such as "chips" made from molded rehydrated potato flakes,
which result In marked structural changes that may have equally marked
effects on the chemical composition of foods.
A-6
TABLE A- 3
Annual Per Capita Intake of Fresh and Processed Fruits,
Potatoes, and Other Vegetables in the United States a
Year
1909
1927
1948
1965
1976
Annual Consumption, kg/ Per son
Fruits
75.6
76.5
73.8
47.3
52.7
Vegetables
(Excluding Potatoes)
Fresh Processed Fresh Processed
3.61
8.1
19.8
27.5
36.5
83.7
85.5
82.8
63.5
65.3
7.7
11.7
21.15
29.7
31.1
Potatoes
Fresh Processed
81.9
63.9
50.0
30.6
24.3
0.2
0.2
0.2
5.4
9.9
a Adapted from Page and Friend, 1978.
These striking changes in the food supply need to be taken into
account when one examines the relationship between diet and cancer.
On the one hand, any change in cancer incidence resulting from major
changes in food processing that occurred before 1900 (e.g., roller
milling of grain) or up to 40 years ago (e.g., flour enrichment) would
probably have been observed long before now. Conversely, because of
the long latent period between exposure and manifestation of cancer,
effects from changes introduced less than 10 years ago might not yet be
evident. If, as is often the case, changes in food-processing methods
are poorly monitored, the extent of exposure to substances resulting
from those processes will not be known. In such cases, it will be
difficult to make any associations between those substances and cancer
incidence.
A more difficult problem is encountered in case-control studies:
here one must determine what foods were consumed by subjects one or
more decades in the past. It is necessary to make one of two assump-
tions when collecting such information: that people can accurately
remember their typical dietary patterns of 10 or more years ago, or
that present diets adequately reflect diets consumed in the past. Both
of these assumptions are most subject to inaccuracies when there have
been continual shifts in the numbers, types, and varieties of available
foodstuffs. Even when the kinds and amounts of foods consumed in the
past can be accurately determined, their chemical composition remains
unknown and may have changed significantly over the decades. For
example, a frozen pizza made with imitation cheese, tomato extender,
and soy-protein "pepperoni" is composed of a very different collection
of chemicals than the apparently similar product made 10 years earlier
with mozzarella cheese, tomato paste, and meat sausage.
A-7
The proportion of manufactured products in the average diet has
been increasing, especially in developed countries, but the detailed
composition of many of these products is not known. Manufacturers
often consider it proprietary information. Figures on the production
of ascorbic acid illustrate both the scale of the potential effects
of processing and the difficulty of monitoring such effects (Table ' A-4) .
During the past 20 years, there has been a sixfold increase in the
tonnage of ascorbic acid produced. But in standard food composition
tables prepared by the U.S. Department of Agriculture, only the amount
of ascorbic acid used for food fortification is recorded. The disposi-
tion of the remainder is unknown. Most of the imbalance is probably
consumed in the form of vitamin supplements. Nonetheless, the fact
remains that large amounts of ascorbic acid, as well as other nutrients,
are added to foods for "technical" reasons, e.g., for their antioxidant
properties, as opposed to "nutritional" reasons. These amounts do not
show up on tables of nutritional value, although vitamins are monitored
more carefully than most other components of the food supply. Most non-
nutritive substances are not monitored at all, and as a consequence
almost nothing is known about their presence or fluctuations over time.
Saccharin, for example, is a nonnutritive substance intentionally added
to food by manufacturers or by the consumers themselves and, to a
very large extent, it is knowingly consumed. Yet, in epidemiological
studies it has proved very difficult to obtain reliable data on indi-
vidual saccharin intake. Obviously, it is even more difficult to
obtain consumption data for substances that are neither monitored, as
are the nutrients, nor consumed intentionally, as is saccharin.
TABLE A-4
Production of Ascorbic Acid in the United States 3
Amount Produced
Year (Metric Tons)
1960 2,392
1965 3,914
1970 5,470
1974 10,054
1982 14,800 (estimated)
*Data from U.S. International Trade Commission, 1980.
A-8
Because of this paucity of information, it is possible to make
only the crudest assessments of factors that may affect the composition
of foods. For example, one can determine whether fruits are available
fresh, frozen, or canned, whether potatoes are available fresh or dried,
but not whether macaroni contains soy flour or whether tomato paste
contains modified starch, 6-carotene (for color), and added vitamin
C among other things*
It is not clear whether all the changes in the food supply have
increased, decreased, or had no effect on the incidence of cancer.
Overall U.S. cancer rates at most sites other than lung and stomach
have remained relatively stable for several decades. This might
suggest that the food supply has contained an unchanging cluster of
cancer-causing or protective substances throughout much of this per-
iod, despite the extensive changes in the composition and quantity
of many of the foods consumed. It is also possible that any changes
capable of affecting cancer rates (positively or negatively) have
occurred too recently to be reflected in cancer statistics. But even
if cancer rates rise or fall in the future, it may prove very diffi-
cult to identify which, if any, specific compositional modifications
are involved, since so many different changes are going on simultane-
ously. This is illustrated in Figures A-2 and A-3, which show the
changing sources of fat in the U.S. diet. These figures reveal that
the relatively stable consumption of "total table spreads" and "total
cooking fats" masks a dramatic shift in the sources and, hence, the
composition of the fats involved. The use of butter and lard has
decreased sharply, whereas margarine and shortening (usually based on
vegetable oil) have come into much wider use (Brewster and Jacobson,
1978).
20
o
C
&
CO
cr
O
O
15
10
j I
1910
1930
1950
1970
YEAR
1976
A-9
o
0>
a
1
C/5
<
cc
a
o
25 r~
20
15
Fats
Shortening
\
\ Lard
\
\
\
1910
1930
1950
1970 k
1976
YEAR
FIGURE A-3. Intake of cooking fat. From Brewster and Jacobson, 1978.
At any particular time, cancer rates probably reflect the sum of
many changes, some producing positive and others negative effects. For
example, the introduction and subsequent wide use of refrigeration and
the increased use of mold-inhibitors and antioxidants have probably had
positive effects. Together, these changes have markedly decreased the
population's exposure to rancid and/or moldy foods and to foods
preserved by salting, smoking, or drying.
The effect of other changes is less clear. Although there has been
relatively little change in the overall percentage of calories derived
from fat, protein, and carbohydrate, there have been marked shifts in
consumption patterns frbm vegetable to animal protein, from complex to
simple carbohydrates, atid, as already noted, from animal to vegetable
fats. The increase in per capita intake of fat from meat has compen-
sated for a decline in the intake of dairy fats. Iri addition, there
has been a marked increase in the intake of separated vegetable oils
that have been structurally altered by hydrogenation and other
treatments.
A-10
There have also been changes in the nature of the fat-soluble
contaminants present in the diet. In federal inspections for pesti-
cide residues, contaminants have been found most frequently in meats
and fats (U.S. Food and Drug Administration, 1980). The Comptroller
General (1979) reported that "of 143 drugs and pesticides likely to
leave residues in raw meat and poultry, 42 were known to cause or
suspected of causing cancer 4" Twenty years ago, fats were much less
likely to carry such residues since the use of both drugs in animals
and pesticides has increased markedly in the interim (Smith, 1980).
A fivefold increase in the per capita intake of french-fried
potatoes is part of a trend toward a much greater consumption of
products crisped by exposure to heated fat or to extreme dry heat.
Such products include potato chips, fried snacks, crackers, and
ready-to-eat breakfast cereals. Many products of such browning
reactions have proved to be mutagenic in laboratory tests as have
the by-products resulting from the frying and broiling of meat and
fish (see Chapter 13). Hence, products in this category must be
regarded as potential contributors to carcinogenesis.
Several other changes may also be important, but their effects on
carcinogenesis are not known. For example, there has been a documented
decline in the consumption of certain types of vegetables, especially
in their fresh state. The effect, if any, of the marked increase in
the consumption of cooked (and often burned) tomatoes is also unclear
as is the effect of the documented decline in the consumption of fresh
cabbage, since the total long-term consumption of other cruciferous
vegetables (e.g., broccoli, cabbage, and kale) is impossible to cal-
culate given the lack of accurate data on home production. However,
the documented decrease in the annual per capita intake of sweet
potatoes, from 11.1 kg per person during 1976 to 2.4 kg during 1980,
combined with the declining consumption of fresh dark green and deep
yellow vegetables, has very likely decreased the intake of dietary
fiber and naturally occurring g -carotene, which recently have been
studied for their possibly protective roles in carcinogenesis (Chapters
8 and 9).
Despite (or perhaps because of) the paucity of information pertain-
ing to the composition of our contemporary food supply, foods have been
most often used in epidemiological studies as indicators of the presence
of particular nutrients or they have been grouped for analysis accord-
ing to certain nutrients they have in common. Given the multitude of
other chemicals present in the diet, it is notable that epidemiological
studies have found significant relationships between the occurrence of
cancer and estimated intakes of such nutrients as fat, vitamins A and
C, or protein (see Chapters 5, 6, and 9). This would seem to indicate
either that these nutrients must play a role in the development of
cancer or that they serve as indicators of other substances that do.
Epidemiological associations between cancer and nutrients are
often based on the presence in the diet of certain foods. For
example, citrus fruits have sometimes been used as indicators of
A-ll
the presence of vitamin C, although they obviously have much more in
common than ascorbic acid. They contain, among other substances,
flavonoids (Chapters 13 and 15). The dietary presence of vitamin A has
often been based on green and yellow vegetable consumption (Chapter 9),
although the active agent in those foods may not actually be vitamin
A. Peto et al. (1981) suggested that carcinogenesis may be inhibited
by g-carotene (the plant constituent that can be converted to vitamin A
in the body), rather than by the vitamin itself. Their report suggests
that, when examining naturally occurring compounds in foods, we should
not limit our attention to those already identified as having a nutri-
tional role.
Until fairly recently, fiber was also overlooked as a possible
protective factor in carcinogenesis. For many years, fiber was re-
garded as a collection of inert substances in foods, even though it was
known to be present in relatively large amounts, compared to vitamins
and minerals. These substances were even regarded as a nuisance factor
that might interfere with the absorption of minerals in unrefined diets.
Since most traditional diets contain large amounts of such indigestible
residues, fiber came to scientific attention as a result of observa-
tions that peoples consuming "primitive" diets high in complex carbohy-
ates (including fiber) appear to be spared a number of maladies, includ-
ing bowel cancer, that are common to populations consuming more refined
diets.
These simple observations have led to ongoing investigations con-
cerning which components of carbohydrate should "count" as fiber, which
of them might play a role In carcinogenesis, and how (or whether) fiber
affects the incidence of certain diseases or whether it acts merely by
displacing other dietary substances that are either carcinogens or
promoters of carcinogenesis.
The recent findings concerning fiber remind us again that sub-
stances in food other than those presently classified as nutrients may
be Instrumental in the development of cancer. Milk Is one major food
that Is difficult to classify In cancer studies. As a source of
vitamin A (Mettlin and Graham, 1979), whole milk may be a beneficial
component of the diet; but as a source of fat (Blair and Fraumeni, 1978;
Howell, 1974), it may have deleterious consequences. The category
"dairy products" or "milk products" may combine milk products such as
butter, cheese, cream, yogurt, low^-fat milk, and cottage cheese, some
of which are very different from each other in composition. In a case-
control study conducted by Phillips (1975), dairy products other than
milk were associated with breast cancer. Hirayama (1977) reported that
the ingestion of two glasses of milk daily was associated with a lower
risk of gastric cancer in a large cohort.
There have been surprisingly few studies linking specific foods
with either increases or decreases in cancer rates. Where there have
been such studies, e.g., those on cruciferous vegetables, the data
A-12
underscore the fact that it will be difficult for epidemiologists to
sort out the specific chemicals of concern. For example, the consti-
tuents of cruciferae responsible for their apparent effect on the
occurrence of cancer may be, as Chapter 15 suggests, indoles, isothio-
cyanates, or other nonnutritive substances demonstrated to affect car-
cinogenesis in the laboratory. But it is not yet possible to attribute
the epidemiological associations to any such substances simply because
of the simultaneous presence in these vegetables of such other consti-
tuents as fiber, 3-carotene, ascorbic acid, or calcium.
Moreover, the identification of these associations is complicated
not only by the composite nature of single foods but also by the in-
terrelated variations in the intakes of a number of foods in any given
diet. By eating more broccoli, one ordinarily eats less of something
else. More broadly, those who increase their consumption of vegetable
products must, of necessity, simultaneously reduce their consumption of
animal products since these are the only two classes of substances
(other than table salt and water) ordinarily consumed by humans. A
reduced intake of animal products will normally result in a decreased
consumption of nutrients such as animal fat, animal protein, heme iron,
preformed vitamin A, and zinc; of mutagens formed during the cooking of
meat; and of such fat-soluble contaminants as pesticides and drugs used
for animals. This tendency for certain nutrients and other substances
to occur together in certain types of foods accounts for the strong
direct correlations among such dietary variables as beef, all meats,
animal fat, and animal protein in epidemiological studies. Moreover, a
reduced intake of animal products is necessarily accompanied by an
increased intake of substances such as starches, fibers, and certain
vitamins and minerals that are present in the substituted vegetable
foods. Since all these dietary constituents increase and decrease
simultaneously, it is difficult to determine which ones, if any, are
involved when, for example, consumption of animal products and cancer
rates decrease simultaneously or when control subjects consume more
animal products than do cancer cases.
Individual diets are not composed of isolated substances or even
isolated foods but, rather, they contain thousands of unique combina-
tions of nutrients and other compounds that comprise the individual
food items. From the standpoint of public education and public health,
therefore, it is considerably less important to identify isolated com-
pounds that cause or protect against certain cancers than it is to
identify dietary patterns that enhance or minimize overall risk. The
conclusions and recommendations contained in Chapter 1 reflect this
committee's assessment of the evidence regarding some components of
these patterns.
SUMMARY AND CONCLUSIONS
Since the turn of the century, there have been extensive changes
in foodstuffs consumed by the U.S. population. Only a few of these
A-13
changes have been measured, and then only crudely. Levels of nutrient
intake that have been monitored have remained relatively constant
between 1909 and the present, but data indicate that this constancy
obscures major unmeasured changes in intake of other substances result-
ing from the declining consumption of certain commodities; changes in
the forms in which foods are consumed; or the introduction of entirely
new products and substances.
The relationship between these changes in the food supply and the
incidence of cancer is not yet clear. The fact that the food supply
has undergone major changes while the rates of cancer at most sites
have been relatively constant may suggest that none of the changes has
an effect on cancer incidence, that the changes have occurred too
recently to produce an effect, or, more likely, that some changes have
had a positive and some a negative impact. Data reviewed in this re-
port indicate that a number of substances in food other than nutrients
may play a role in the causation or the prevention of cancer. Thus, it
may be important in epidemiolgical studies to consider a variety of
food classifications and to monitor changes in the food supply in
addition to those that affect nutrients.
A-14
REFERENCES
Blair, A., and J. F. Fraumeni, Jr. 1978. Geographic patterns of
prostate cancer in the United States. J. Natl. Cancer Inst.
61:1379-1384.
Brewster, L. M., and M. Jacobson. 1978. The Changing American Diet.
Center for Science in the Public Interest, Washington, B.C. 80 pp.
Comptroller General. 1979. Problems in Preventing the Marketing of
Raw Meat and Poultry Containing Potentially Harmful Residues.
Comptroller General's Report to the Congress of the United States,
No. HRD-79-10, April 17, 1979. General Accounting Office,
Washington, D.C. 87 pp.
Hirayama, T. 1977. Changing patterns of cancer in Japan with special
reference to the decrease in stomach cancer mortality. Pp. 55-75 in
H. H. Hiatt, J. D. Watson, and J. A. Winsten, eds. Origins of Human
Cancer, Book A: Incidence of Cancer in Humans. Cold Spring Harbor
Laboratory, Cold Spring Harbor, N.Y*
Howell, M. A. 1974. Factor analysis of international cancer
mortality data and per capita food consumption. Br. J. Cancer
29:328-336.
Mettlin, C., and S. Graham. 1979. Dietary risk factors in human
bladder cancer. Am. J. Epidemiol. 110:255-263.
Molitor, G. T. T. 1980. The food system in the 1980s. J. Nutr.
Educ. 12 (Suppl. 1) :103-111.
Page, L., and B. Friend. 1978. The changing United States diet.
BioScience 28:192-197.
Peto, R., R. Doll, J. D. Buckley, and M. B. Sporn. 1981. Can
dietary carotene materially reduce human cancer rates? Nature
290:201-208.
Phillips, R. L. 1975. Role of life-style and dietary habits in risk
of cancer among Seventh-Day Adventists. Cancer Res. 35:3513-3522.
Smith D. T. 1980. Antibiotic additives: The prospect of doing without.
Farmline 1(9):14~15.
U.S. Food and Drug Administration. 1980. Compliance Program Report
of Findings. FY 77 Total Diet Studies Adult (7320.73). Bureau of
A-15
Foods, Food and Drug Administration, U.S. Department of Health,
Education, and Welfare, Washington, D.C. [33] pp.
U.S. International Trade Commission. 1980. Synthetic Organic
Chemicals. United States Production and Sales, 1980. USITC
Publication 1183. Office of Industries, U.S. International Trade
Commission, Washington, D.C. 327 pp.
CHAPTER 4
TOTAL CALORIC INTAKE
This chapter reviews the many experiments in which the variable
studied is the total amount of food humans or animals eat, rather than
the precise composition of their diet. It is entitled "Total Caloric
Intake," although it is difficult to determine whether the effects
brought about by changing the quantity of a diet are due to the result-
ing changes in caloric intake or to the changed distribution of specific
nutrients.
A number of factors complicate the interpretation of the effect of
caloric intake on cancer incidence. Caloric density can be modified
either by modifying the ratio of fat (9.5 kcal/g) to carbohydrate (4.0
kcal/g) or by varying the concentration of nonnutritive bulk (fiber).
Since dietary fat and fiber may also affect carcinogenesis, it becomes
difficult to measure any independent effect of calories.
It is also not possible to identify the effect of caloric intake on
cancer incidence in studies of humans. Although total caloric intake by
two populations can be compared, the interpretation of the data is lim-
ited by the same considerations that apply to experiments in animals. It
is also difficult to interpret studies in which the prevalence of obesity
is compared with cancer incidence. Obesity is related to the balance
between caloric intake and caloric expenditure. However, the proportion-
al contributions of caloric intake and caloric expenditure to cancer risk
are not known. Furthermore, there is evidence that obesity is related to
the consumption of diets with increased caloric density. Thus, the contri-
butions of fat, fiber, and carbohydrate cannot be readily measured inde-
pendently.
EPIDEMIQLOGICAL EVIDENCE
There are few epidemiological data relating total caloric intake to
cancer risk, partly because most dietary studies have been based on
preselected food lists, which do not permit the quantification of total
dietary intake.
Berg (1975) pointed out that the international distribution of hor-
mone-dependent cancers has generated suspicion that these cancers may
be -related to affluence. e suggested that diets typical of affluent
populations, when itigestei since Childhood, could over stimulate the en-
docrine system, lead to aberrations in metabolic processes, and result
in cancer.
4-2
Gregor t_ al^. (1969) analyzed data on caloric intake and the inci-
dence of gastric and intestinal cancers. They concluded that as the per
capita food intake (or gross national product) increases, the mortality
rates for gastric cancers fall and those for intestinal cancer rise.
Hill <et_ al. (1979), who studied mortality from colorectal cancer in three
socioeconomic groups in Hong Kong, found that the most affluent group had
more than twice the mortality of the poorest group, i.e., 26.7/100,000
vs. 11.7/100,000. The relative proportions of nutrients in their diets
were similar, but estimated daily caloric intake was 2,700 in the lowest
socioeconomic group and 3,900 in the highest.
In a correlation study conducted by Armstrong and Doll (1975), per
capita total caloric intake was examined in relation to cancer incidence
in 23 countries and to cancer mortality in 32 countries. Significant
correlation coefficients (r 5-0.70) were found for total calories and
rectal cancer incidence in males, leukemia in males, and mortality from
breast cancer in females. Notably, the per capita intake of calories was
highly correlated with intakes of total fat, total protein, and animal
protein. The finding for breast cancer was reproduced by Gaskill et al.
(1979), who analyzed data on mortality from breast cancer in relation to
per capita intake for foods by state within the United States. However,
there was no correlation when they controlled for age at first marriage
(to reflect age at first pregnancy) in the analysis.
In two case-control studies, a number of dietary variables, including
total caloric and fat intake, were estimated for subjects with cancer of
the breast (Miller t_ alU , 1978), for subjects with cancer of the colon
and rectum ( Jain ^Jt_ j^. , 1980), and for matched controls. For breast
cancer cases, Miller and colleagues found no association with caloric
intake and a weak association with total dietary fat. Jain and coworkers
reported direct associations with caloric intake for both colon and rec-
tal cancer, but the associations were not as strong as they were for in-
take of saturated fat. The authors concluded that the relevant variable
in each study was more likely to be dietary fat than caloric intake.
Independent associations of breast cancer with body weight and height
were found by de Waard and Baanders-van Halewijn (1974) in a cohort study
of postmenopausal women in the Netherlands. Also, differentials in
weight between cases of breast cancer and controls were found in Taiwan
(Lin et_al. , 1971) and in Sao Paulo, Brazil (Mirra et^ al^. , 1971). Thus,
de Waard (1975) suggested that susceptibility to breast cancer could be
related to body mass (which, in turn, could be related to nutrition), but
this hypothesis has not been accepted universally (MacMahon, 1975). Sub-
sequently, de Waard et_ al^ (1977) examined the influence of height and
weight on age-specific incidence of breast cancer in the Netherlands and
Japan and computed age-specific incidence curves for different height and
weight groups. The heavier and taller postmenopausal women had the high-
est incidence of breast cancer. However, there appeared to be little
independent effect of weight if there was an adjustment for its correla-
tion with height. In his earlier study, de Waard (1975) suggested that
4-3
lean body mass may be the important variable. However, if height is
critical (and it is critical to the calculation of lean body mass) ,
nutritional factors, if relevant, must begin to operate during adoles-
cence or earlier, as was pointed out by MacMahon (1975). De Waard et al.
(1977) suggested that approximately one-half of the differences in inci-
dence of breast cancer between Holland and Japan can be attributed to
differences in body weight and height.
In an analysis based on a long-term prospective study conducted by
the American Cancer Society from 1959 to 1972, Lew and Garfinkel (1979)
examined the relationship between mortality from cancer and other
diseases and variation in weight among 750,000 men and women selected
from the general population. Cancer mortality was significantly elevated
in both sexes only among those 40% or more overweight. For men, most of
the excess mortality resulted from cancer of the colon and rectum; for
women, cancer of the gallbladder and biliary passages, breast, cer-
vix, endometrium, and ovary were the major sites. It was not possible
to evaluate the relative importance of overweight in comparison to total
caloric intake or intake of other nutrients. Therefore, it cannot be
assumed that obesity as such is the major risk factor. Nonetheless, most
studies confirm a relationship between obesity and caloric intake, and in
the absence of definitive information from studies that have separated
the effects of caloric intake and fat intake, e.g., Miller et_ _aJ. (1978)
and Jain et_ al_. (1980) (discussed above), it is reasonable to assume that
high total caloric intake is a risk factor for some sites identified in
other studies.
EXPERIMENTS IN ANIMALS
Tannenbaum (1942a,b, 1944, 1945a,b) examined the effects of caloric
restriction upon the development of spontaneous and chemically Induced
tumors in several strains of mice. Growth of benzo[_ajpyrene-induced
tumors was inhibited by caloric restriction to different extents in ABC,
Swiss, or DBA mice (Tannenbaum, 1942a) . The level of dietary fat
affected growth of skin tumors or spontaneous and chemically induced
breast tumors, but not of sarcomas or lung tumors (Tannenbaum, 1942b) .
Caloric intake was restricted by controlling the amount of starch added
to a diet containing commercial ration and skim milk powder. Mice whose
daily dietary intake was 11.7 calories exhibited 25% more spontaneous
mammary tumors than mice whose intake was 9.6 calories (Tannenbaum,
1945a). The incidence of benzpyrene-induced tumors was similar in mice
ingesting 11.7 and 9.6 calories per day, but when caloric intake dropped
to 8.1 calories daily, tumor incidence fell by 38% (Tannenbaum, 1945a) .
Among mice ingesting 11.7 calories daily, those receiving 18% of the
calories from fat developed 70% more spontaneous mammary tumors th$n
those whose diets contained only 2% (approximately 4% of calories) fat.
Tannenbaum concluded that diefeaiy fat exerted a specific influence over
and above its caloric contribution (Tannenbgiutn, 1945b) .
4-4
The influence of caloric restriction was also tested in a study of
3-methylcholanthrene-induced skin tumors in mice fed ad libitum and in a
control group on a restricted diet. The carcinogen was painted on the
skin for 10 weeks, and the mice were then observed for 1 year. On the
basis of this experiment and earlier studies, Tannenbaum (1944, 1945b)
concluded that the carcinogen-induced changes occur regardless of diet,
but that the ad libitum ingestion of diet promotes tumor development.
Lavik and Baumann (1943) studied the promoting action of different
levels of dietary fat on 3-methylcholanthrene-induced skin tumors in
mice. A low fat, low calorie diet resulted in the fewest tumors. Lard
with high (saturated) and low (unsaturated) melting points produced
similar results, and the addition of riboflavin to the diet had a slight
promoting effect; but the principal effect on carcinogenesis was produced
by high caloric intake.
The studies of Tannenbaum and those by Lavik and Baumann could be
profitably extended since we have identified a variety of possible car-
cinogens and promoters and have gained a greater understanding of food
composition in recent decades.
SUMMARY AND CONCLUSIONS
Epidemiological Evidence
The epidemiological evidence supporting total caloric intake as a
risk factor for cancer is slight and largely indirect. Much of it is
based on associations between body weight or obesity and cancer. Studies
that have evaluated both caloric and fat intake suggest that fat intake
is the more relevant variable.
Experimental Evidence
Studies in animals to examine the effect of caloric intake on car-
cinogenesis have been few and are difficult to interpret. In these
experiments, animals on restricted diets developed fewer tumors and their
lifespan far exceeded that of animals fed ad libitum, thereby indicating
a decrease in the age-specific incidence of tumors. However, because the
intake of all nutrients was simultaneously depressed in these studies,
the observed reduction in tumor incidence or delayed onset of tumors
might have been due to the reduction of other nutrients such as fat. It
is also difficult to interpret experiments in which caloric intake has
been modified by varying dietary fat or fiber, both of which may by them-
selves exert effects on tumorigenesis.
Thus, neither the epidemiological nor the experimental studies
permit a clear interpretation of the specific effect of caloric intake
4-5
on the risk of cancer. Nonetheless, the studies conducted in animals
show that a reduction in total food intake decreases the age-specific
incidence of cancer* The evidence for humans is less clear.
4-6
REFERENCES
Armstrong, B., and R. Doll. 1975. Environmental factors and cancer
incidence and mortality in different countries, with special
reference to dietary practices. Int. J. Cancer 15:617-631.
Berg, J. W. 1975. Can nutrition explain the pattern of international
epidemiology of hormone-dependent cancers? Cancer Res.
35:3345-3350.
de Waard, F. 1975. Breast cancer incidence and nutritional status with
particular reference to body weight and height. Cancer Res.
35:3351-3356.
de Waard, F., and E. A. Baanders-van Halewijn. 1974. A prospective
study in general practice on breast-cancer risk in postmenopausal
women. Int. J. Cancer 14:153-160.
de Waard, F. , J. P. Cornells, K. Aoki, and M. Yoshida. 1977. Breast
cancer incidence according to weight and height in two cities of
the Netherlands and in Aichi prefecture, Japan. Cancer
40:1269-1275.
Gaskill, S. P., W. L. McGuire, C. K. Osborne, and M. P. Stern. 1979.
Breast cancer mortality and diet in the United States. Cancer
Res. 39:3628-3637.
Gregor, 0., R. Toman, and F. Prusov^L 1969. Gastrointestinal cancer
and nutrition. Gut 10:1031-1034.
Hill, M., R. MacLennan, and K. Newcombe. 1979. Letter to the Editor:
Diet and large-bowel cancer in three socioeconomic groups in Hong
Kong. Lancet 1:436.
Jain, M., G. M. Cook, F. G. Davis, M. G. Grace, G. R. Howe, and A. B.
Miller. 1980. A case-control study of diet and colo-rectal
cancer. Int. J. Cancer 26:757-768.
Lavik, P. S., and C. A. Baumann. 1943. Further studies on the tumor-
promoting action of fat. Cancer Res. 3:749-756.
Lew, E. A., and L. Garfinkel. 1979. Variations in mortality by weight
among 750,000 men and women. J. Chronic Dis. 32:563-576.
Lin, T. M. , K. P. Chen, and B. MacMahon. 1971. Epidemiologic
characteristics of cancer of the breast in Taiwan. Cancer
27:1497-1504.
4-7
MacMahon, B. 1975. Formal discussion of "Breast cancer incidence and
nutritional status with particular reference to body weight and
height." Cancer Res. 35:3357-3358.
Miller, A. B., A. Kelly, N. W. Choi, V. Matthews, R. W. Morgan,
L. Munan, J. D. Burch, J. Feather, G. R. Howe, and M. Jain.
1978. A study of diet and breast cancer. Am. J. Epidemiol.
107:499-509.
Mirra, A. P., P. Cole, and B. MacMahon. 1971. Breast cancer in an
area of high parity: Sao Paolo, Brazil. Cancer Res. 31:77-83.
Tannenbaum, A. 1942a. The genesis and growth of tumors. II. Effects
of caloric restriction per se. Cancer Res. 2:460-467.
Tannenbaum, A. 1942b. The genesis and growth of tumors. III. Effects
of a high-fat diet. Cancer Res. 2:468-475.
Tannenbaum, A. 1944. The dependence of the genesis of induced skin
tumors on the caloric intake during different stages of
carcinogenesis. Cancer Res. 4:673-677.
Tannenbaum, A. 194 5a. The dependence of tumor formation on the
degree of caloric restriction. Cancer Res. 5:609-615.
Tannenbaum, A. 194 5b. The dependence of tumor formation on the
composition of the calorie-restricted diet as well as on the
degree of restriction. Cancer Res. 5:616-625.
CHAPTER 5
LIPIDS (FATS AND CHOLESTEROL)
EPIDEMIOLQGICAL EVIDENCE
Fats
Of all the dietary factors that have been associated epidemiologi-
cally with cancers of various sites, fat has probably been studied most
thoroughly and produced the greatest frequency of direct associations.
However, since dietary fat is highly correlated with the consumption of
other nutrients that are present in the same foods, especially protein in
Western diets, it is not always possible to attribute these associations
to fat intake per jse with absolute certainty.
Breast Cancer* Several international correlation studies have shown
direct associations between per capita fat intake and breast cancer in-
cidence or mortality (Armstrong and Doll, 1975; Carroll, 1975; Drasar and
Irving, 1973; Gray e al. , 1979; Hems, 1978; Knox, 1977). In general,
the correlations were higher for total fat than for the other dietary
factors considered (e.g., animal protein, meat, specific fat components,
and oils) . Some of the similarities in the findings undoubtedly reflect
the overlapping data sets used in these studies rather than reproduced
results.
In other correlation studies, intracountry data sets have been used
to compare dietary fat intake and breast cancer. Gaskill et_ al^. (1979)
compared per capita intake of various foods by state within the United
States with corresponding breast cancer mortality rates and found a
significant direct correlation with fat intake when results from all
states studied were combined. The correlation disappeared, however,
when the southern states were excluded from the analysis or when they
controlled for age at first marriage (as a reflection of age at first
pregnancy) or median income. Their results suggested that dairy products
as a class increased the risk of breast cancer. Hems (1980) noted that
time trends for breast cancer mortality in England and Wales from 1911
to 1975 correlated best with corresponding per capita intake patterns
for fat, sugar, and animal protein one decade earlier. In studies based
on personal interview data, Kolonel ^ al^. (1981) correlated individual
consumption of fat with ethriic patterns of breast cancer incidence 1m
Hawaii* These investigators found significant associations with total
fat, with animal fat, and with both saturated and unsaturated fats.
The findings of three case-control studies support a role for dif tary
fat in the risk for breast cancer. Phillips (1975) reported a direct
association between frequency of consumption of h|gh~at foods and fef east
cancer in a study of 77 breast cancer cases and matched comtirols among
5-2
Seventh-Day Adventists in California. Miller et^ al. (1978) also found
a weak direct association, but no evidence of a dose response, between
total fat consumption (based on quantitative dietary histories) and
breast cancer in a study of 400 cases and 400 matched neighborhood
controls in Canada.
In the third case-control study, Lubin it aJL. (1981) found signifi-
cant increasing trends in relative risk with more frequent consumption of
beef and other red meat, pork, and sweet desserts. Analysis of computed
mean daily nutrient intake supported a link between breast cancer and
consumption of animal fat and protein.
Nomura et al. (1978) compared the diets consumed by husbands of women
with and wilhoutf breast cancer. (The men were participants in a pro-
spective cohort study of Japanese men in Hawaii.) These investigators
reported a direct association between consumption of high fat diets by
the husbands and breast cancer in their wives, who were assumed to have
adhered to similar eating patterns.
Prostate Cancer. Prostate cancer has also been associated epide-
miologically with fat intake. International data on mortality, but not
incidence, indicate that there is a strong direct correlation of per
capita total fat intake and cancer at this site (Armstrong and Doll,
1975). Howell (1974) reported similar results from a study based on a
rank correlation with mortality in 41 countries. In Hawaii, the Inci-
dence of prostate cancer in four ethnic groups was highly correlated
with consumption of both animal and saturated fat (Kolonel jst al. ,
1981). In the mainland United States, Blair and Fraumeni (1978) corre-
lated prostate cancer mortality by county with dietary variables. They
observed that counties with a high risk for prostate cancer among whites
had correspondingly high per capita fat intakes among the same population.
Hirayama (1977) observed that one of the most notable dietary changes in
Japan since 1950 is increased per capita fat intake and that this change
parallels a striking increase in mortality from prostate cancer.
Prostate cancer has been associated with dietary fat in two case-
control studies. In an ongoing study based on 111 cases with prostate
cancer and 111 matched hospital controls, Rotkin (1977) has found that
the cases had consumed high fat foods with greater frequency than had
the controls. Schuman jejt al. (1982) also reported a more frequent con-
sumption of foods with high animal fat content by cases than by controls.
Cancer of Other Reproductive Organs. Other reproductive organs for
which there have been associations between dietary fat and cancer include
the testes, corpus uteri, and ovary. Armstrong and Doll (1975) found
direct correlations between per capita intake of total fat and incidence
of cancer of the testes and corpus uteri and mortality from ovarian can-
cer. Lingeman (1974) also correlated mortality from ovarian cancer with
international data on fat intake. Kolonel et_ ail. (1981) found a direct
association between ethnic patterns of totaT7 animal, saturated, and
5-3
unsaturated fat consumption In Hawaii and incidence of cancer of the
corpus uteri.
Gastrointestinal Tract Cancer. Dietary fat has also been associated
with cancer at several sites in the gastrointestinal tract. In only one
case-control study, however, has an association of stomach cancer with
dietary fat been suggested. In that study, Higginson (1966) reported
more frequent consumption of fried foods and greater use of animal fats
in cooking by gastric cancer cases than by controls. Graham et al.
(1972) failed to confirm this finding In a subsequent study of 168 gas-
tric cancer cases matched to hospital controls.
Although time-trend data in Japan (Hirayama, 1977) and one inter-
national correlation study (Lea, 1967) have shown associations of fat
intake with pancreatic cancer, most epidemiological data pertain to
cancers of the large bowel. Armstrong and Doll (1975) reported direct
correlations between colon and rectal cancer incidence and mortality and
per capita intake of total fat, based on international data. Knox (1977)
also reported a strong correlation between mortality from cancer of the
large intestine (excluding rectum) and per capita total fat Intake, and
only a slightly weaker correlation between mortality from rectal cancer
and intake of total fat and animal fat.
After reviewing their data from an earlier study, Enig aJL . (1979)
retracted their original suggestion that colon cancer was directly cor-
related with intake of total, saturated, and vegetable fat, but not with
animal fat. Bingham et al. (1979) calculated average intakes of nutrients
by populations in different regions of Great Britain. They found no sig-
nificant association of fat intake with mortality from colon and rectal
cancers. Lyon and Sorenson (1978) also reported little difference in fat
intake between the population of Utah (with a low risk for colon cancer)
and that of the United States as a whole.
The contrast between the strong International correlations and the
lack of associations within countries is striking. One possible expla-
nation is that the regional food intake data within a country are based
on means of individual consumption data and, thus, may be too uniform to
demonstrate any strong association with risk of colon or rectal cancer.
In contrast, the variation In fat Intake among countries Is much greater,
thereby facilitating the demonstration of associations.
MacLennan t al. (1978) compared the diets of adult men in two Scandi-
navian populations with different risks for colon cancer (high risk for
Danes in Copenhagen and low risk for Finns in Kuopio) . These studies,
which were based on food diaries, indicated that the consumption of fat
was similar for both groups, but that there were differences in fiber
intake (see Chapter 8). Reddy et_ al^ (1978) also studied this low risk
Finnish population and compared their diets to those o'f a high risk
population In New York* They too found no difference between groups in
5-4
total fat intake, but noted that a higher proportion of total fat was
consumed as dairy products by the Finns and as meat by the New Yorkers.
This observation raises the possibility that the source as well as the
quantity of dietary fat may be relevant.
In a case-control study conducted in parallel with the study on
breast cancer (described above), Phillips (1975) found a direct asso-
ciation between colon cancer and the frequent consumption of high-fat
foods by Seventh-Day Adventists. In a study of cases and hospital con-
trols among blacks in California, Dales et al. (1978) observed a direct
association between risk of colon cancer and frequent consumption of
foods high in saturated fat. The association was strongest for those
who consumed diets high in saturated fat and low in fiber content. Total
fat consumption, estimated from frequency data, was also reported to be
higher among large bowel cancer cases than among controls in a study
conducted in Puerto Rico (Martinez et_ al. , 1979).
Dietary histories were used to estimate nutrient intake in a case-
control study conducted by Jain et al. (1980) in Canada. They reported
a direct association (including a dose response) between risk of both
colon and rectal cancer and consumption of fat, especially saturated
fat. The elevated risks persisted after adjustment for other nutrients
in the diet.
Several reports on meat consumption are relevant to this discussion
since meat can be an important source of dietary fat, especially satu-
rated fat. Berg and Howell (1974) and Howell (1975) reported a high
correlation between colon cancer mortality and meat intake (particularly
beef), based on international per capita intake data. In Ha waii f investi-
gators reported a direct association between frequency of meat, especially
beef, consumption and large bowel cancer among Japanese cases and hospital
controls (Haenszel et^ al. , 1973) . This finding was not reproduced in
studies conducted in Buffalo, New York (Graham t al. , 1978) and in Japan
(Haenszel al^ > 1980), nor in parallel cohorts followed prospectively
in Minnesota and Norway (Bjelke, 1978). Furthermore, Enstrom (1975) has
noted that trends in beef intake in the United States do not correlate
with trends in the incidence of and mortality from colorectal cancer.
Meat consumption has also been associated with pancreatic cancer.
In a case-control study conducted in Japan, Ishii et ail . (1968) found a
direct association between meat consumption by men and mortality from
pancreatic cancer. Their findings were based on responses to mailed
questionnaires, most of which were completed by relatives of deceased
cases. Hirayama (1977) reported a relative risk of 2.5 for daily meat
intake and incidence of pancreatic cancer in a prospective cohort study
of 265,118 Japanese.
Summary . The results from a substantial number of epidemiological
studies have indicated an association between dietary fat and cancers of
the gastrointestinal tract (especially the large bowel) and of endocrine
target organs (especially the breast and prostate). Some studies of
5-5
large bowel cancer were conducted on groups of relatively homogeneous
populations, and some were not specifically designed to test the hypothe-
sis that fat consumption Is associated with colon cancer. The studies
designed specifically to test this hypothesis (e.g., Dales _et, aJ.. , 1978;
Jain et al., 1980) tended to show the most striking direct associations,
especially" when the possible confounding effects of dietary fiber were
considered. The evidence for cancer of the breast and prostate is more
consistent than that for large bowel cancer. The results of the most
thorough case-control study of breast cancer yet reported (Miller et^ a 1 . ,
1978) were only weakly positive, however, partly reflecting the fact that
recent food consumption was measured rather than dietary intake patterns
earlier in life, which may have been the more relevant exposure period.
(Studies of changing breast cancer incidence among Japanese migrants to
the United States and their descendents, for example, suggest that
early-life exposures are important determinants of breast cancer risk.)
Cholesterol
High-fat diets have been associated with atherosclerosis a condition
that has also been associated with elevated serum cholesterol levels.
Therefore, there has been Interest in studying the relationship of serum
cholesterol levels as well as cholesterol intake to the incidence of can-
cer. Most of the studies described below were designed to examine the
association between cholesterol and cardiovascular disease, and were not
specifically intended to measure cancer incidence or mortality. However,
the opportunity provided by these long-term studies of cardiovascular
disease in which serum cholesterol levels of the subjects were determined
at the beginning of the study has resulted In a number of different re-
ports on observed associations.
Using per capita food intake data from 20 industrialized nations and
simple correlation analysis, Liu et al. (1979) showed that there was a
strong direct correlation between per capita Intake of total fat and
cholesterol and the mortality rate for colon cancer, but that there was
an inverse correlation for fiber intake. Cross-classification showed a
highly significant association for cholesterol, but not for fat or fiber.
These Investigators suggested that the data support a causal relationship
between dietary cholesterol and colon cancer.
Pearce and Dayton (1971) conducted an 8-year clinical trial In which
groups of 422 and 424 men were fed a conventional diet or one containing
high levels of polyunsaturated fat (to lower cholesterol levels), respec-
tively. Incidence of cancer deaths In the groups on the experimenta.1
diet was higher* In a similar experiment conducted in Finland, Miettirien
*Li* (1972) also found more carcinomas in the test group. A study
group, convened to examine cancer incidence In men from five controlled
trials of cholesterol-lowering diets, found little difference in relative
risks (Ederer et al., 1971).
5-6
In other studies, clofibrate, a hypolipidemic agent, or a placebo was
administered to more than 10,000 volunteers between 30 to 54 years of age
whose serum cholesterol levels were in the top tertile (Committee on Prin-
ciple Investigators, 1978). The total mortality from causes other than
ischemic heart disease was substantially higher in the clofibrate group:
there was a disproportionately large number of neoplasms of the gastroin-
testinal tract and a few more neoplasms in the respiratory tract. How-
ever, there were too few cancer deaths to demonstrate a statistically
significant difference among the test groups.
In another study of the relationship between colon cancer and serum
cholesterol, Rose et_ al.. (1974) observed that the initial levels of serum
cholesterol in colon cancer patients were lower than expected. They also
reported that serum cholesterol levels were higher in patients with cancer
of the stomach, pancreas, liver, bile ducts, and rectum than in the con-
trols. Bjelke (1974) reported a similar correlation between colon cancer
and low levels of serum cholesterol. Nydegger and Butler (1972) examined
total serum cholesterol levels in 186 controls and 122 subjects with
malignant tumors. Their data also generally showed lower cholesterol
levels in the cancer patients.
Beaglehole et_ l. (1980) studied the relationship between serum
cholesterol concentration and mortality in New Zealand Maoris over a
period of 11 years. They found significant inverse relationships be-
tween serum cholesterol concentrations and cancer mortality.
In a 7. 5-year follow-up study of London civil servants, Rose and
Shipley (1980) observed that mortality from cancer at all sites was
associated with a progressive decline in plasma cholesterol levels.
These investigators grouped cancer deaths into those that occurred
less than 2 years after the subjects entered the study and those that
occurred from 2 to 7.5 years afterward. For the group in which deaths
occurred within 2 years, the age-adjusted mortality rate for those with
the lowest plasma cholesterol levels was more than double the rate for
those with the highest levels. However, cancer deaths among those
followed for longer than 2 years occurred at the same rate, regardless
of plasma cholesterol level at entry into the study. The investigators
concluded that the decline in cholesterol levels was probably a meta-
bolic consequence of cancer, which, while unsuspected, was present when
the subjects entered the study.
In more than 5,000 subjects studied for 24 years in the Framingham
Heart Study (Williams et^ al. , 1981) , an inverse relationship between
serum cholesterol levels and cancer of the colon and other sites was ob-
served in men but not in women.
Kark et_ a.IL. (1980) related serum cholesterol levels to cancer inci-
dence in moreTthan 3,000 individuals followed for as long as 14 years in
Evans County, Georgia. Patients diagnosed as having cancer at any site
at least 1 year following entry into the study had had entry serum cho-
lesterol levels significantly lower than those in the noncancer patients*
5-7
This association was the same for black and white females and for black
and white males, but was stronger in males of both races. The possibility
that the presence of cancer may have been responsible for the lower serum
cholesterol levels was investigated. Patients were categorized into
three groups, depending on when evidence of cancer was first observed
after entry into the study: within 1 year, from 1 to 6 years, and from 7
to 13 years. Initial serum cholesterol levels were higher in the first
group than in the other two groups, but no differences were noted between
the latter groups. Kark and colleagues also observed little difference
in cholesterol levels in cases and controls when various cancer sites
were grouped together. However, they did report low serum cholesterol
levels in lung cancer patients, whereas Stamler t al. (1968) observed
that serum cholesterol levels were higher in lung cancer cases than in
controls. A study conducted in Norway indicated that there was no over-
all relationship between serum cholesterol levels and total cancer inci-
dence (Westlund and Nicolaysen, 1972).
In the Honolulu Heart Study, 598 deaths were observed in 7,961 men
whose cholesterol levels had been determined and who were followed for 9
years (Kagan et al. , 1981) . The baseline serum cholesterol levels were
directly assocTated with mortality from coronary heart disease but in-
versely associated with total cancer mortality, mortality from cancers of
the esophagus, colon, liver, and lung, and malignancies of the lymphatic
and hematopoietic systems.
In Yugoslavia, Kozarevic et al. (1981) related baseline serum choles-
terol levels to mortality in 11,121 males over a 7-year period. The in-
verse association between cancer deaths and serum cholesterol levels was
not statistically significant.
In the Puerto Rico Heart Health Programme, 9,824 men were followed
for 8 years (Garcia- Palmier i e auL. , 1981). Serum cholesterol levels mea-
sured at the first examination were found to vary inversely with subse-
quent mortality from cancer.
Peterson jet al. (1981) followed 10,000 men in Sweden for a mean of
2.5 years. They found that deaths from neoplastic disease and other
noncoronary heart disease peaked at Ibw levels of serum cholesterol.
In contrast, serum cholesterol was not associated with overall risk
of death from cancer in three epidemiological studies of Chicago men
(Dyer jet_ al. , 1981). When cancer deaths were evaluated by site, there
was a significant inverse association between serum cholesterol and
deaths from sarcoma, leukemia, and Hodgkin f s disease in the nearly 2,000
men studied for 17 years, but not for deaths from lung cancer, colorectal
cancer, cancer of the oral cavity, pancreatic cancer, or all other can-
cers combined. There was, however, a suggestion of a direct association
for breast cancer in women.
These studies have been assessed by Lilienfeld (1981) and by others*
who concluded that the observed inverse correlations do not substantiate
5-8
any direct cause-and-effect relationship between low blood cholesterol
levels and cancer.
Only one case-control study has specifically evaluated serum choles-
terol levels In cases of colon cancer and matched controls (Miller et_
al., 1981). In 133 pairs matched by age and sex, serum cholesterol
levels were lower for cases than for controls. However, following
stratification by tumor stage, significant differences in cholesterol
levels persisted only between cases with advanced tumors and controls.
Furthermore, only women, not men, had significantly lower serum choles-
terol levels with advancing disease. The lack of an association In early
disease supports the concept that low serum cholesterol levels observed
in colon cancer patients may be the result of a metabolic change accom-
panying tumor growth and may not necessarily precede tumor formation.
Miller e a 1 . (1978) studied the association of dietary levels of
cholesterol and breast cancer. They found no significant differences
in estimated cholesterol consumption between cases and controls. In
another case-control study, the same group found that cholesterol Intake
for males with rectal cancer and females with colon and rectal cancer was
higher than for controls ( Jain et^ aJU , 1980). Although the relative risk
for dietary cholesterol was significant at higher intakes for all male
and female cases, compared to all controls, it was substantially less
than the estimates of risk for other nutrients associated with intake of
fat, especially saturated fat.
There is an apparent conflict in the evidence, i.e., that an in-
creased risk of cancer of the colon and other sites has been associated
not only with dietary cholesterol (and simultaneous intake of other,
possibly more relevant lipid components) but also with very low serum
cholesterol levels. A possible explanation might be that a high intake
of dietary fat (and/or cholesterol) by persons whose metabolism maintains
low serum cholesterol results in reduced biosynthesis of cholesterol and
a high rate of excretion for cholesterol breakdown products in the
intestine (Lin and Connor, 1980). These breakdown products could serve
as substrates for the intraluminal production of carcinogens by intes-
tinal bacteria (Hill et al . , 1971). However, in metabolic studies con-
ducted in hospital wardTs, low serum cholesterol is usually accompanied by
excretion of low levels of bile acid. This observation is not compatible
with the mechanisms normally proposed for the carcinogenic effect of
dietary lipids.
In summary, data pertaining to the association between serum
cholesterol levels and total cancer incidence and mortality are incon-
sistent. An inverse correlation between serum cholesterol levels and
colon cancer in men has been noted in some studies, but not in all. It
is not clear whether lower than normal serum cholesterol levels are the
cause, or whether they reflect the metabolic consequences, of cancer.
Thus, the data are inconclusive and do not point to a causal relationship
between low cholesterol levels and risk of colon cancer. However, since
5-9
they do suggest that low serum cholesterol levels may be a clue to some
unknown factor, possibly something that is transported in the low density
lipoprotein fraction of serum, these data and future findings should be
examined carefully.
RELATIONSHIP OF FECAL STEROID EXCRETION TO BOWEL CARC1NQGENESIS
The possibility that metabolites in the colon could provide a clue to
the presence of malignancy has stimulated a number of investigators to
study the level and spectrum of steroids in the feces of populations at
low or high risk for colon cancer, as well as of animals fed colon car-
cinogens together with various dietary regimens. The amounts of neutral
and acidic fecal steroids correspond to the level of fat intake. How-
ever, studies of the ratios of primary to secondary bile acids or the
ratio of cholesterol to its metabolic products (i.e., coprostanol and
coprostanone) have revealed no significant differences among the popula-
tions studied (Moskovitz et_ al^. , 1979; Mower et^ aiU , 1979; Reddy, 1979).
Recent comparisons of high risk and low risk populations, e.g., three
socioeconomic groups in Hong Kong (Hill t_ al. , 1979) and Finns and New
Yorkers (Reddy, 1979), suggest that the concentration of bile acids is
elevated in feces of the groups that are at higher risk.
Pioneering efforts by Hill and his colleagues (1971) pointed to an
association between rates of mortality from colon cancer and fecal
excretion of bile acids as well as the fecal degradation of cholesterol
and its metabolites. They revived an earlier concept, based on struc-
tural and steric /similarities, that bile acids might be transformed to
the carcinogen 3-methylcholanthrene by anaerobic gut bacteria. In the
studies leading to these earlier theories, deoxycholic acid was converted
chemically to 3-methylcholanthrene by Wieland and Dane (1933) and by Cook
and Haslewood (1933). Later, Fieser and Newman (1935) derived the same
carcinogen from cholic acid. The chemical steps used in these studies
were all reactions known to occur naturally, i.e., oxidation, hydrogena-
tion, cyclization, and dehydrogenation, although laboratory conditions
for the synthesis did not reproduce normally encountered biological
conditions.
Through the efforts of Hill, Reddy, Mastromarino, Narisawa, Nigro,
their coworkers, and others, the concept has evolved that fecal bile
acids and metabolites of cholesterol may function as cocarcinogens,
carcinogens, or promoters in tumorigenesls of the large bowel (Hill gt_
al. , 1971; Mastromarino t al_. > 1976; Narisawa al. , 1974; Nigro et
al, 1973; Reddy and Wynder, 1973; Reddy et^ aJL. , 197 7a). To date, how-
ever, no act;ive carcinogen derived from bile acids has been isolated
from human or animal feces.
Reddy ^^al* (197 7a) demonstrated that a fourfold increase in dietary
(from 5% to 20%) given to rats increased the 24-hour fecal excretion
5-10
of neutral and acid sterols by 30% to 40% (based on body weight). Bac-
terial conversion of primary to secondary bile acids occurred more exten-
sively in rats fed the high fat diet than in those fed the low fat diet.
The possibility that bile acids may have tumor-promoting effects is
supported to some extent by the finding that bile acids affect cell ki-
netics in the intestinal epithelium. Diversion of biliary and pancrea-
tic secretions from the intestine decreases DNA synthesis and cell pro-
liferation (Fry and Staffeldt, 1964; Ranken e aJL . , 1971; Roy et al. ,
1975), whereas the administration of secondary bile acids increases cell
proliferation in liver bile ducts and the biliary tract epithelium
(Bagheri e al. , 1978). Inhibition of DNA synthesis and cell prolifer-
ation has also been observed in the rat colon following biliary diversion
(Deschner and Raicht, 1979).
Possible promotional effects of bile acids on bowel tumorigenesis
were suggested in studies initiated by Narisawa et^ al. (1974) and com-
pleted, with a large sampling of bile acids, by RedcFp and colleagues
(see review by Reddy et_ l/ > 1980). In these studies, N-methyl'-N 1 -
nitro-N-nitrosoguanidine (MNNG) , which is a direct-acting carcinogen,
was administered intrarectally to conventional or germfree rats for 2
weeks. During the subsequent 16 weeks, 20 mg doses of sodium etiolate,
sodium chenodeoxycholate, or sodium lithocholate in 0.5 ml of peanut oil
were administered intrarectally to rats 3 times a week. No tumors were
detected in the control groups. The total number of large bowel tumors
in each of the conventional and germfree rats given intrarectal instilla-
tions of bile salts was greater than in rats given MNNG without bile
salts. These data also suggest that gut microflora was not required
for the effect of bile acids to be manifested. In this study, the
quantity of bile salts administered intrarectally was approximately 20
to 60 times higher than that normally excreted in the feces during a
24-hour period. Perhaps more importantly, the instillations at levels
of approximately 100 mM were at least 10 times higher than the normal
concentrations of these salts within the lumen of the bowel.
Palmer (1979) observed that bile salts interact readily with mem-
branes from artificial liposomes, bacteria, and mammalian cells. The
well-studied cytotoxic effects of bile salts are invariably preceded by
alterations in membrane permeability in red blood cells, in a variety of
tissues, and in mucosal cells of both the large and the small intestine
(Dawson and Isselbacher, 1960; Dietschy, 1967; Hoffman, 1967). In one
study, the effects of these salts upon permeability (and presumably
cytotoxicity) in the gut were minimized when conjugated bile salts were
added to the unconjugated bile salts in sufficiently high concentrations
(Low-Beer e ail. , 1970). Thus, it cannot be determined whether the
effects of intrarectally instilled unconjugated bile salts demonstrated
classic tumor promotional activity or resulted from nonspecific damage
and repair activity associated with increased cellular proliferation of
the colonic mucosa induced by the high intraluminal concentration of the
salts.
5-11
Cohen and associates studied the effect of bile acid on colon tumors
induced by nitro some thy lurea (NMU) by feeding rats lab chow pellets with
and without added bile acid. They observed that 0.2% cholic acid (Cohen
e al. , 1978), but not chenodeoxycholic acid (Raicht e al. , 1975), in-
creased the number of NMU-induced colon tumors, as compared to the num-
ber of tumors in rats fed nonsupplemented pellets. In the dimethylhydra-
zine (DMH) model, no effect on colon tumorigenesis was observed in rats
fed 0.3% cholic acid in a semisynthetic diet (Broitman, 1981).
Evidence that increased quantities of bile acids in the colonic lumen
were associated with an increase in azoxymethane (AOM)~ induced colon
tumorigenesis in rats was provided by Chomchai et al. (1974). Williamson
et a 1 . (1979) showed that bile initiated prompt ileal hyperplasia in rats
following intestinal resection with diversion of the pancreatic and bil-
iary ducts to the terminal ileum, i.e., pancreatobiliary diversion.
Feeding cholestyramine to rats given AOM for tumor induction increased
the average number of tumors in the large bowel but not in the small bowel
(Nigro et_ _al. , 1973, 1977). Vahouny e -al. (1981) demonstrated that in-
traluminal infusion of 165 yM of cholic, deoxycholic, and chenodeoxycholic
acids 1:1:1 twice daily for 5 days resulted in severe topological changes
in the colonic mucosa.
Thus, the enhancement of tumorigenesis observed at high concentra-
tions of bile acids may be related to nonspecific effects of tissue
injury. Tumor- enhancing effects of nonspecific injury have been attrib-
uted to increased cellular proliferation, which accompanies inflammation
and repair (Ryser, 1971).
EXPERIMENTAL EVIDENCE
The first demonstration that dietary fat could influence tumorigene-
sis was reported by Watson and Mellanby (1930). Most of these studies
were conducted by increasing the level of dietary fat, which also led to
an increase in the total intake of calories. Addition of 12.5% to 25.0%
butter to a basal (3% fat) diet given to coal-tar-treated mice increased
the incidence of skin tumors from 34% to 57%. Similarly, Lavik and
Baumann (1941, 1943), who administered 3-methylcholanthrene topically to
mice found that a basal diet, when supplemented with 15% fat (shortening),
increased the yield of skin tumors from 12% to 83%. Fat was especially
effective when fed 6 to 12 weeks after treatment with a carcinogen. Com-
paring diets containing 10% corn oil, 10% coconut oil, or 10% lard for
their ability to enhance tumors, these investigators observed a minor
effect of unsatuifation: the incidence of tumors at 5 months was 33% (for
control diets), 61% (for added lard diets), 66% (for added coconut oil
diets) j and 76% (for added corn oil diets).
Mammary Tumors
Tatrnenbaum (1942) demonstrated that dietary fat enhanced the develop-
ment of either chemically or spontaneously induced mammary tumors in mice.
5-12
The incidence of spontaneous tumors was greater when the high fat diets
were instituted at 24 weeks of age than when they were fed beginning at
38 weeks. Tannenbaum and Silverstone (1957) noted that tumor incidence *
was greater in obese mice than in normal mice and that caloric restric-
tion inhibited mammary tumorigenesis in normal mice. This was also
observed by Waxier and colleagues, who induced obesity in mice with gold
thioglucose and observed that spontaneous mammary carcinomas developed
more quickly in obese mice than in controls (Waxier, 1954; Waxier et. al., '
1953). After reducing the weight of the obese mice below that of con~ i
trols (which were also treated with gold thioglucose) by limiting their
dietary intake, they observed a decrease in mammary tumors compared to
controls. The effects of caloric restriction on reducing the incidence |
of chemically induced tumors can be negated by increasing the dose of the
carcinogen (King et aJL . , 1949; Tannenbaum and Silverstone, 1957; White,
1961; White et_ al. , 1944). By feeding mice isocaloric high and low fat >
diets, Tannenbaum (1942) provided evidence that fat, rather than calories
per se, was responsible for enhancing tumorigenesis. This observation
differed from the findings of Lavik and Baumann (1943), who reported that I
the caloric content of the diet had a greater effect than the level of
fat on the induction of skin tumors in mice by 3-methylcholanthrene.
These earlier studies have been comprehensively reviewed by Tannenbaum >
(1959), Tannenbaum and Silverstone (1957), and Carroll and Khor (1975).
In 1970, Carroll and Khor again pointed out that the level of dietary I
fat was as important as the amount of 7, 12-dime thy lbenz[a_] anthracene j
(DMBA) administered to induce breast cancer. They studied the effect of \
both high and low doses of the carcinogen fed to rats in corn oil. At I
the low dose (1 mg), rats fed a 20% corn oil diet exhibited more tumors
and a shorter latent period, but no difference in the number of tumors
per tumor-bearing rat, as compared to rats fed a 0.5% corn oil diet. <
When the dose of DMBA was increased to 2.5 mg, the high fat diet in- j
creased tumor incidence and the number of tumors, but did not alter the I
latent period.
Jr
The quality or type of lipid was also shown to be an important factor
in the induction of breast cancer by DMBA (Carroll and Khor, 1971). The
incidence of tumors at this site was uniformly high with all dietary fats |
tested at a level of 20% in the diet, but the number of tumors per group ;
and per tumor-bearing rat was proportionally greater in the rats fed un- \
saturated fats. Furthermore, it was apparent that the yield of tumors |
per group was also influenced by the level of essential fatty acid
linoleic acid present in the fat. Groups of rats fed tallow or coconut r
oil (which are inadequate sources of linoleate) had significantly fewer I
tumors than groups fed polyunsaturated fats (which are adequate sources
of linoleate). Because the enhancement of breast tumorigenesis by high
fat diets was observed when the diets were fed after tumor initiation by *
DMBA, the investigators concluded that dietary fat exerted its effect
during the promotional phase (Carroll, 1980). As the dose of carcinogen
was increased, the promotional effect of high fat diets became stronger. i
There is a limit to the promotional effects of dietary f at s> however, .
5-13
since diets containing fat at levels greater than 20% were no more
effective than those containing 20%.
The enhancement of DMBA-induced mammary tumorigenesis in rodents by
high fat diets (especially those containing polyunsaturated fats) has
been observed by a number of Investigators (Carroll and Khor, 1971;
Hopkins and West, 1976; Ip, 1980; King e al. , 1979). More recently,
Carroll and coworkers found that saturated fat was as effective as
polyunsaturated fat in enhancing tumorigenesis when a small quantity of
polyunsaturated fat (3% sunflower seed oil) was added to the saturated
fat (17% coconut oil) (Carroll, 1975; Carroll and Hopkins, 1979; Hopkins
and Carroll, 1979). They also learned that the polyunsaturated fat used
must provide sufficient amounts of essential fatty acids and that the
diet must contain high levels of total fat to increase the yield of
breast tumors. Whether these two requirements are interrelated is not
certain. But studies In rats have shown that essential fatty acid
metabolism and accumulation of polyunsaturated fat in tissues is
Influenced by dietary fat (Mohrhauer and Holman, 1967; Peifer and Holman,
1959).
Providing support for an association between dietary fat and DMBA-
induced breast cancer are findings from studies in rats with the known
breast carcinogen NMU. Chan e ail. (1977) observed a significant re-
duction in the latent period for the development of NMU-induced breast
tumors in female Fischer 344 rats fed high fat diets compared to rats
fed low fat diets. However, unlike the studies using the DMBA model of
breast carcinogenesis, high fat diets increased only the Incidence and
not the multiplicity of NMU-induced breast tumors.
In a study of the relationship of dietary fat levels to x-ray-induced
and NMU-induced mammary carcinogenesis, Sllveraan et_ al/ (1980) reported
similar effects. The incidence and multiplicity of breast tutors induced
by 350 rads of total body irradiation were increased in Sprague-Dawley
rats fed a calorie-controlled, 20% lard diet, compared to rats fed a 5%
lard diet. The high fat diet increased the multiplicity of NMU-induced
tumors, but not the incidence.
Both the level and the quality of dietary fat appear to influence the
growth rate of DMBA-induced breast tumors, according to studies by McCay
i* (1980). Rats fed a diet containing a high level of polyunsaturated
fat (20% corn oil) exhibited an average tumor growth rate that was con-
siderably greater than that for rats fed a diet containing high levels of
saturated fat (18% coconut oil and 2% linoleic acid). In animals fed a
low fat diet (2% linoleic acid), the average tumor growth rate was mai;k-
edly lower than the rates for the other two groups* Thus, the tumor
growth rate appears to be determined in part by the total dietary fat and
In part by the polyunsaturated fat content. Therefore, a given dose of
DMBA could produce a similar number of initiated cells In the, maiomary
gland, independent of the dietary regimen used, and the number of tumors
that are palpable within a fixed time would depend on the growth rate of
the initiated clones. Consequently, if a higher level of total dietary
5-14
fat or of polyunsaturated fat accelerated clonal growth, the number of
tumors reaching palpable size within a fixed time would be greater.
Growth of transplantable tumors is also influenced by dietary fat.
A transplantable mammary adenocarcinoma developed much more readily in
host mice fed a high level of polyunsaturated fat than in mice fed an
equivalent level of saturated fat (Hopkins and West, 1977). In a study
by Abraham and Rao (1976), as little as 1.0% corn oil added to the diet
stimulated the growth of a transplantable mammary tumor in mice. By
using inhibitors of prostaglandin biosynthesis, these investigators
concluded that this effect was related to the level of essential fatty
acids, rather than to synthesis of prostaglandin. Pure linoleic acid in
the diet at 0.1% was as effective as 15% corn oil in enhancing the growth
of a transplantable mammary adenocarcinoma (Hillyard and Abraham, 1979).
In studies of cell cultures with and without added polyunsaturated fat,
Kidwell et^al^. (1978) and Wicha et_ al . (1979) demonstrated that polyun-
saturated fat enhanced the growth of both normal and neoplastic mammary
epithelial cells from rats. Corwin e aJU (1979) measured the tumori-
genicity of Kirs ten sarcoma virus-transformed murine cell line, AK3T3,
which was grown in delipidized tissue culture media. Its tumorigenicity
(incidence of tumors following implantation of a constant number of cells)
in BALB/c mice was compared to that in a conventional line of FK3T3 cells
maintained in a complete tissue culture medium. Although sarcomas in
general are not responsive to diet, an increase in tumorigenicity was
observed with AK3T3 cells as the level of dietary polyunsaturated fats
was increased from 4% to 8%, whereas an opposite effect on tumorigenicity
was noted with the FK3T3 cells. Thus, lipid supply .in vitro affected the
expression of the transformed phenotype of a transplantable tumor. This,
in turn, altered the response of the tumor to dietary lipids in the host.
Rogers (1975) and Newberne and Zeiger (1978) observed that the
effects of a high fat diet on breast carcinogenesis could be modified
when the diet was marginal in lipo trope (choline and methionine)
content. In Sprague-Dawley rats given 2-acetylaminof luorene (AAF) or
DMBA to induce breast tumors, the tumor incidence was lower and death
from the tumors occurred later in marginally lipotrope-def icient rats
than in controls.
Hepatic and Pancreatic Cancer
When administered to Fischer rats, which are resistant to breast
cancer, AAF induced hepatic carcinomas (Newberne and Zeiger, 1978).
Under these conditions, a high fat diet that was marginally deficient
in lipo tropes significantly increased the incidence of hepatic carcino-
mas, as compared to the incidence in rats fed a high fat diet with
adequate lipotropes. Thus, the effect of marginal lipotrope deficiency
on the relationship between dietary fat and carcinogen-induced tumori-
genesis appeared to differ from one target organ to another.
An increase in dietary fat increased* the incidence of AAF-induced
hepatomas in male rats (Sugai et al. , 1972). Farber (1973) suggested
5-15
that chronic feeding of AAF resulted in the cloning of hepatic cells with
resistance to AAF toxicity. Hyperplastic nodules that result from the
regenerative activity of such clones ultimately progress to form hepato-
mas. McCay et a.L. (1980) studied the influence of dietary fat in the
early stages of hyperplastic nodule formation and during the later stages
of hepatoma development. Hyperplastic nodules formed from AAF more
frequently and the latent period was shorter in rats fed a low fat diet
(2% linoleic acid) than in rats fed diets with high saturated fat (18%
coconut oil and 2% linoleic acid) or with a high polyunsaturated fat con-
tent (20% corn oil). In contrast, there was a 100% incidence of hepatomas
in the rats fed the high polyunsaturated fat diet, a 20% incidence in
those fed the low fat diet, and high mortality among those fed the high
saturated fat diet because of the excessive toxicity of AAF under these
conditions. These studies illustrate the differing effects of dietary
fat upon the various stages of hepatoma development.
Dietary lipids also modify aflatoxin-B^-induced liver tumors in
rats (Newberne et al., 1979). When beef fat was fed to rats, the number
of tumors induced was the same, regardless of whether the beef fat was
fed only after induction (51%) or both before and after induction (53%).
Feeding of polyunsaturated fat (corn oil) before and after induction
resulted in a 100% tumor yield, but when the oil was fed only after tumor
induction, the yield was 66%. The authors concluded that unsaturated
fats increase the tumor yield more effectively than do saturated fats,
but that this effect may occur during the initiation or early promotional
phase of hepatic carcinogenesis.
Dietary fat may modify the incidence of pancreatic adenocarcinomas
induced in rats by azaserine (Longnecker et^ aJL , 1981; Roebuck et al.,
1981). In Lewis rats fed diets containing either 20% corn oil or 20%
saf flower oil, the number of pancreatic neoplasms was higher than in
animals fed the same percentage of saturated fat. The animals fed the
control diet (5% corn oil) and treated with azaserine exhibited the same
incidence and numbers of pancreatic neoplasms as did animals fed an 18%
saturated fat diet. Compared to controls, there was a marked increase in
hepatocellular carcinomas in rats given azaserine but maintained on a
lipotrope-deficient diet.
Intestinal Cancer
A variety of compounds that are carcinogenic in the bowel have been
used in a number of animal models to study the effect of dietary fat on
tumorigenesis at that site. Nigro j*t l. (1975) demonstrated that
Sprague-Dawley rats treated with AOM developed more intestinal tumors
and more metast^tic: lesions when fed a diet containing 35% beef fat than
when fed regular chpw. Siiice the caloric density of the beef fat diet
was significantly greater than that of the laboratory chow, it is diffi-
cult to sort out the effect of calories from that of fat on tumori-
genesis. Nevertheless, the report provided a model for studying diet-
responsive intestinal tumorigenesis.
5-16
Reddy e a!L. (1974) used DMH to induce tumors of the colon (and, to a
lesser extent, small intestine) in rats fed 5% or 20% lard or corn oil
diets. Rats fed the 5% corn oil diets had a greater tumor incidence and
higher average number of tumors per animal than those fed the 5% lard
diet. Tumor incidence and multiplicity increased with the higher levels
of dietary fat. However, rats fed the 20% fat diets exhibited essentially
the same incidence and multiplicity of tumors whether the fat was polyun-
saturated or saturated. In a repeat study with animals maintained on
these diets for two generations before tumor induction with DMH, findings
were essentially the same (Reddy et. al . , 1977a). Measurements indicated
that there were no differences in the quantities of diet consumed daily
among all the dietary groups. Since the caloric density of low and high
fat diets differed, rats eating the high fat diets consumed, in addition
to more fat, approximately 20% more calories.
In a study by Broitman e al^. (1977), atherogenic diets containing 5%
or 20% coconut oil were fed to rats given DMH to induce tumors^ of the
bowel. These investigators also observed that rats fed the 20% saturated
fat diet had a greater incidence and multiplicity of tumors than those
fed the 5% saturated fat diet. However, they pointed out that rats fed
the low fat diet consumed fewer calories, gained much less weight, and
thus received less of the carcinogen than did rats fed the high fat
diets.
Studies with a number of strains of rats and various carcinogens
have illustrated that intestinal tumorigenesis is enhanced as the quan-
tity of dietary fat is increased. Bansal t al. (1978), using Wistar
Furth rats and DMH for tumor induction, noted that rats fed 30% lard
developed more large bowel tumors than did those fed a low fat standard
diet. To induce colon tumorigenesis in Fischer 344 rats, Reddy and
associates (I977b, 1980) administered DMH or methylazoxymethanol (MAM)
acetate systemically on a weight basis or gave the animals constant
intrarectal doses of 2 f ,3-dimethyl-4-arainobiphenyl (DMAB) or NMU.
These investigators demonstrated that the tumor incidence in rats fed
20% beef fat was greater than that in those fed 5% beef fat, irrespec-
tive of the carcinogen used to induce the intestinal tumors. Since the
routes of metabolic activation for some of these carcinogens differ, it
is more likely that the effects of increased levels of dietary fat were
manifested following activation of the carcinogen, rather than during
the various steps leading to activation.
Promoting effects of dietary fat were suggested by studies in which
high fat diets increased the frequency of small and large bowel tumors
when fed to rats after administration of AOM but not before or during
administration of the carcinogen (Bull et^ al. , 1979). The high fat
diet (30% beef fat) used in these studies had a caloric density that was
approximately 34% greater than the low fat diet (5% beef f at) , and was
considered by the authors to be responsible for the differences in weight
gains between groups fed the high and low fat diets.
5-17
Cruse !, (1978) suggested that dietary cholesterol may be
cocarcinogenic. Rats given DMH and fed a diet of liquid Vivonex (an
amino acid hydrolysate) with added cholesterol had shorter lifespans,
decreased time to tumor appearance, and more colonic tumors per rat than
did the animals fed Vivonex alone. Because these dietary regimens are so
different from those consumed by humans, the applicability of these find-
ings to human health is not clear.
Broitman et a 1 . (1977) studied effects of serum cholesterol levels
on DMH-induced tumorigenesis in the bowel. Sprague-Dawley rats were fed
isocaloric cholesterol-containing diets supplemented with either 20%
coconut oil to promote hypercholesterolemia and vascular lipidosis or 20%
saf flower oil to maintain lower serum cholesterol levels and, presumably,
to shunt cholesterol through the gut. Rats fed the 20% polyunsaturated
fat diet experienced less vascular lipidosis but developed more bowel
tumors than did rats fed the saturated fat diet. It could not be ascer-
tained from these studies whether the enhanced bowel tumorigenesis was
due to the polyunsaturated fat per or whether the effects were related
to its hypocholesterolemic action. Reddy and Watanabe (1979) observed
that the intrarectal administration of cholesterol, cholesterol-5, 6-
epoxide, or cholestane-3,5,6-triol did not exert or lead to any tumor-
promoting activity in rats given MNNG to induce bowel tumors.
The number of DMH-induced intestinal tumors was greater in rats fed
diets marginally deficient in the lipotropes choline and methionine than
in rats fed high fat diets with adequate amounts of lipotropes (Rogers
and Newberne, 1973)*
To date, an active carcinogen derived from bile acids has not been
isolated from human or animal feces. The proposed mechanisms for the
action of bile acids on bowel tumorigenesis are discussed earlier in this
chapter*
SUMMARY
Epidemiological Evidence
Fats. There is some epidemiological evidence for an association
between dietary fat and cancer at a number of sites, but most of the evi-
dence pertains to three sites: the breast, the prostate, and the large
bowel. In various populations, both the high incidence of and mortality
from breast cancer have been shown to correlate strongly with higher pei:
capita fat intake; the few case-control studies conducted have also shown
this association with dietary fat. Like breast cancer, increased risk of
large bowel cancer has been associated with higher fat intake in both
correlation and case-control studies. The data on prostate cancer are
more limited, but they top suggest fchat an increased risk is related to
high levels of dietary fat. In general, it is not possible to identify
specific components of fat as being clearly responsible for the observed
effects, although total fat and saturated fat have been associated most
frequently*
5-18
The epidemiological data are not entirely consistent. For example,
the magnitude of the association of fat with breast cancer appears
greater in the correlation data than in the case-control data. This may
reflect the fact that recent dietary intake was assessed in the case-
control studies, whereas dietary patterns much earlier in life may have
had a greater influence on breast cancer risk. Furthermore, some studies
of large bowel cancer did not show an association with dietary fat, possi-
bly because they either focused on relatively homogeneous populations or
were not specifically designed to test the hypothesis that fat intake is
associated with cancer. Indeed, the studies designed specifically to
test this hypothesis tended to show the most striking direct correlations,
especially when the possible confounding effects of dietary fiber were
taken into consideration.
Cholesterol. The relationship between dietary cholesterol and cancer
in humans is not yet clear. Many studies of serum cholesterol levels and
cancer mortality have indicated that there is an inverse association with
colon cancer in males, but the evidence is inconsistent and is not suffi-
cient to establish a causal relationship. Furthermore, other explanations
for the observations are possible. For example, low serum levels could
be the result rather than the cause of the cancer.
Relationship of Fecal Steroid Excretion to Bowel Carcinogenesis
In most reports on the association of dietary fat and bowel carcino-
genesis, it is generally assumed that dietary fat acts as a promoter. To
date, this effect has been examined in only one report, which suggested
that high lipid diets may promote bowel tumorigenesis. High fat diets
increased tumor yields more effectively than low fat diets when fed after
the administration of a bowel carcinogen but not before. It is not clear
if the effects observed were related to consumption of lipids or calories.
Increasing the quantity of dietary fat fed to rats increases the
total quantity of bile acids and neutral sterols excreted in the feces.
There is no evidence that bile acids or neutral sterols per se can be
converted in vivo to carcinogens or cocarcinogens by the fecal flora
under any dietary conditions.
Regardless of the carcinogen used to initiate bowel tumors, expo-
sures of the colonic lumen to a direct flow of bile, resin-bound salts,
or direct intrarectal instillation of bile salts have been consistently
associated with a higher number of tumors than in control animals.
Colonic tissue damage may result from exposure to the abnormally
high quantities and/or concentrations of bile salts used in these
studies. Thus, it is not possible to determine whether the enhancing
effect of bile salts on colon tumorigenesis is promotion or the result
of nonspecific tissue injury.
5-19
Although most of the data suggest that dietary fat has promoting
activity, there is little or no knowledge concerning the specific mecha-
nisms involved in tumor promotion. Furthermore, there is not enough
evidence to warrant the complete exclusion of an effect on initiation.
Experimental Evidence
Mammary Tumors . In studies of breast cancer, the influence of lipid
nutriture on tumorigenesis follows a consistent pattern, regardless of
whether the tumors are chemically induced, occur spontaneously, or result
from tumor cell implantation.
Increasing the level of dietary fat from 5% to 20% increases the
yield and/or incidence of chemically induced breast tumors, depending
on the carcinogen used. Breast tumorigenesis is enhanced when high fat
diets are fed after, but not before, tumor initiation. This is consis-
tent with the concept that dietary fat exerts a promoting effect on
tumorigenesis rather than an effect at the initiation stage. At low
doses of the carcinogen, high fat diets decrease the latent period and
increase tumor incidence. At high doses of carcinogen, high fat diets
increase the incidence and numbers of tumors, but have no effect on
latency.
In a few studies using isocaloric diets, various levels of dietary
fat have been administered. It is possible that enhanced tumorigenesis,
associated with increasing levels of dietary fat, may be related to a
nonspecific increase in caloric intake. Mammary tumorigenesis is en-
hanced by obesity and is inhibited by restriction of total food intake.
Diets containing 20% polyunsaturated fat enhance tumorigenesis more
effectively than saturated fat, provided that it serves as an adequate
source of essential fatty acids. Supplementation of a high saturated
fat diet with 3% polyunsaturated fat provides the same tumor-enhancing
effects as a 20% polyunsaturated fat diet. Thus, the possible promoting
effects of high-lipid diets on breast carcinogenesis depend upon the
total quantity of fat in the diet (with the maximum effect achieved at
20%) and sufficient polyunsaturated fat to serve as an adequate source
of essential fatty acids. Llpid requirements for enhanced growth of
transplantable breast adenocarcinomas are essentially the same as those
described above. Limited data on normal and neoplastic rat mammary
epithelial cells in cell culture also indicate that essential fatty acids
are required for maximal cell growth.
Hepatic and Pancreatic Cancer. Increasing dietary lipids increases
the incidence of carcinogen-induced hepatomas. Differing effects of the
quality and quantity of dietary fat depend upon the stage of hepatoma
development at the time of exposure. Hepatic tumorigenesis, unlike
breast carcinogenesis, is enhanced by lipotrope deficiency. Limited data
5-20
indicate that the tumor yield of hepatomas and pancreatic neoplasms is
increased more effectively by polyunsaturated fat than by saturated fat,
Intestinal Cancer* Increasing the quantity of dietary fat (generally
from 5% to 20%) increases the incidence and yield of bowel tumors' induced
by a variety of carcinogens, including DMH, AOM, MAM acetate, DMAB, MNNG,
and NMU. Data on the association of dietary lipids and tumorigenesis are
more consistent for the large bowel than for the small intestine. Studies
comparing the effects of high and low dietary fat on tumorigenesis iti the
bowel rarely used isocaloric diets or pair-feeding studies. Consequently,
it is equally possible that the tumor-enhancing effect of high fat diets
at this site may be related to increased consumption of calories. At
dietary fat levels of 5%, polyunsaturated fat appears to have a greater
tumor-enhancing effect than does the equivalent level of saturated fat.
At 20% dietary fat levels, there is no clear difference between the
effects of polyunsaturated fat and saturated fat on bowel tumorigenesis.
General Summation of Experimental Evidence* In summary, numerous
experiments on animals have shown that dietary lipid influences tumori-
genesis in the breast and the colon. Its effects on the liver and the
pancreas have been studied in a few experiments. An increase in total
dietary fat from 5% to 20% of the weight of the diet (i.e., approximately
10% to 40% of total calories) is associated with a higher tumor incidence
in each of these tissues; conversely, animals consuming low fat diets
have a lower tumor incidence. When total fat intake is low, polyun-
unsaturated fats appear to be more effective than saturated fat in
enhancing tumorigenesis; however, the effect of polyunsaturated fats
becomes less prominent as total dietary fat is increased to 20% of the
diet. Dietary fat appears to affect tumor promotion rather than tumor
initiation, although an effect on initiation cannot be excluded. The
specific mechanism involved in tumor promotion is not known, although
some evidence suggests that colon cancer is associated with enhanced
secretion of certain bile steroids and bile acids.
Experimental data on cholesterol and cancer risk are too limited to
permit any inferences to be drawn.
CONCLUSIONS 1
The committee concluded that of all the dietary components it
studied, the combined epidemiological and experimental evidence is most
-'-The Committee on Diet, Nutrition, and Cancer judged the evidence asso-
ciating high fat intake with increased cancer risk to be sufficient to
recommend that consumption of fat be reduced (see Chapter 1). Two years
ago, the Food and Nutrition Board stated in its report Toward Healthful
Diets (National Academy of Sciences, 1980) that "there is no basis for
making recommendations to modify the proportions of these macronutrients
(e.g., fat] in the American diet at this time."
5-21
suggestive for a causal relationship between fat intake and the occur-
rence of cancer. Both epidemiological studies and experiments in animals
provide convincing evidence that increasing the intake of total fat in-
creases the incidence of cancer at certain sites, particularly the breast
and colon, and, conversely, that the risk is lower with lower intakes of
fat. Data from studies in animals suggest that when total fat intake is
low, polyunsaturated fats are more effective than saturated fats in
enhancing tumorigenesis, whereas the data on humans do not permit a clear
distinction to be made between the effects of different components of fat.
In general, however, the evidence from epidemiological and laboratory
studies is consistent.
5-22
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Tannenbaum, A. 1942. The genesis and growth of tumors. III. Effects
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Homburger, ed. The Physiopathology of Cancer, Second edition.
Paul B. Hoeber, Inc., New York.
Tannenbaum, A., and H. Silverstone. 1957. Nutrition and the genesis
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Waxier, S. H. 1954. The effect of weight reduction on the occurrence
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5-33
Waxier, S. H., P. Tabar, and L. R. Melcher. 1953. Obesity and the
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Westlund, K. , and R. Nicolaysen. 1972. Ten-year mortality and
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White, F. R. 1961. The relationship between underfeeding and tumor
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Res. 21:281-290,
White, F. R., J. White, G. B. Mider, M. G. Kelly, W. E. Heston, and
P. W. David. 1944. Effect of caloric restriction on mammary-tumor
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Wicha, M. S., L. A. Liotta, and W. R. Ridwell. 1979. Effects of free
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CHAPTER 6
PROTEIN
Dietary protein has often been associated with cancers of the
breast, endometrium, prostate, colorectum, pancreas, and kidney.
However, since the major dietary sources of protein (such as meat)
contain a variety of other nutrients and nonnutritive components, the
association of protein with cancer at these sites may not be direct
but, rather, could reflect the action of another constituent
concurrently present in protein-rich foods.
EPIDEMIOLOGICAL EVIDENCE
Armstrong and Doll (1975) examined incidence rates for 27 cancers
in 23 countries and mortality rates for 14 cancers in 32 countries and
correlated them with the per capita intake of a wide range of dietary
constituents and other environmental factors. These investigators
reported relationships between many of these variables. For example,
the correlations of total protein and animal protein with total fat
were 0.70 and 0.93, respectively, whereas correlations with the gross
national product were 0.32 and 0.65. In a study that analyzed diet
histories of more than 4,000 subjects, Kolonel et^ al^. (1981) observed
that the correlation between total protein and total fat consumption
was 0.7.
Breast Cancer
In the study by Armstrong and Doll (1975) mentioned above, per
capita intakes of total protein and animal protein were significantly
correlated with the incidence of and mortality from breast cancer. In
a similar study, Knox (1977) compared per capita intakes of individual
foods and nutrients with the chief causes of mortality in 20 different
countries: Canada, the United States, Japan, and 17 European countries.
His results also indicated that there was a strong correlation between
the per capita intake of animal protein and mortality from breast can-
cer. Armstrong and Doll (1975) found that there was a stronger asso-
ciation for animal protein than for total protein, and in both of these
studies, the correlations of breast cancer with per capita total fat
intake were generally as strong or stronger than those for animal
protein.
Hems (1978) correlated 1970^1971 mortality rates for breast cancer
iti 41 countries with per capita food intake for 1964-1966. He found a
direct correlation with intake of protein, total fat, and calories from
animal products, independent of other components of the diet* However,
time-trend data for breast cancer mortality and per capita food intake
6-2
in England and Wales supported the association with fat more strongly
than the association with protein (Hems, 1980). Gray et_ al_. (1979)
analyzed International incidence and mortality rates for breast cancer
in relation to per capita intake of animal protein. They found a
direct correlation, even after controlling for height, weight, and age
at menarche.
Gaskill et^ al. (1979) examined age-adjusted breast cancer mortality
in relation to per capita intake for certain foods by state within the
United States. Although they found a direct correlation between breast
cancer mortality and per capita protein intake, this finding was not
statistically significant after controlling for age at first marriage
(as an indicator of age at first pregnancy). Kolonel et_ al_. (1981)
found a direct correlation between consumption of animal protein and
the incidence of breast cancer in five different ethnic groups in
Hawaii based on diet histories obtained by Interview.
Of three case-control studies of diet and breast cancer, signi-
ficant direct associations with dietary fat only were found in two
(Miller e al_. , 1978; Phillips, 1975), whereas direct associations
with both animal fat and protein were found in the third (Lubln et^
al., 1981).
Large Bowel Cancer
Gregor et l. (1969) reported a direct correlation between per
capita intake of animal protein and mortality from Intestinal cancer
in 28 countries. Armstrong and Doll (1975) observed that per capita
intake of total protein, animal protein, and total fat were all strong-
ly correlated with the Incidence of and mortality from colon and rectal
cancer for both sexes. Their findings for cancer at. these sites were
similar to those for breast cancer (i.e., there were stronger correla-
tions for total fat and for animal protein than for total protein) .
These authors also reported a strong association between the Intake
of eggs and cancer of the colon and rectum. This association was
greater than that for total protein. In contrast to these direct
correlations, Bingham et^ al. (1979) found no significant association
for intakes of animal protein In a study correlating the average
intakes of foods, nutrients, and fiber in different regions of Great
Britian with the regional pattern of mortality from colon and rectal
cancers.
Jain et^ jQ. (1980) reported the only case-control study of large
bowel cancer In which protein was specifically examined. Although
these investigators found a direct association between consumption of
high levels of protein and risk of both colon dnd rectal cancer, they
found a stronger association for saturated fat.
The relationship of meat Intake to risk of colorectal cancer has
been examined in a number of studies, but protein intake per se was not
6-3
estimated In most of them. However, because meat is a major source
of protein in the Western diet, findings in these studies may reflect
associations with protein. Berg and Howell (1974) and Howell (1975)
correlated international mortality rates for colon cancer with per
capita intake data and found the strongest correlations for meat,
especially beef. In a study by Armstrong and Doll (1975), the corre-
lations were stronger for meat than for total protein and animal pro-
tein. In studies of the relationship between certain foods and cancer
of the large intestine, Knox (1977) reported the strongest correlations
for eggs, followed by beef, sugar, beer, and pork. In contrast, time-
trend data for per capita beef intake and colorectal cancer incidence
and mortality in the United States showed no clear association (Enstrom,
1975).
Haenszel et_ jal. (1973) studied cases of large bowel cancer and
hospital controls among Japanese in Hawaii. They found an associa-
tion between cancer at this site and consumption of legumes, starches,
and meats. The association was strongest for beef. A similar study
among Japanese in Japan (Haenszel _et_ aJ. , 1980) did not reproduce these
findings, nor did parallel case-control studies conducted in Norway and
Minnesota (Bjelke, 1978) and at the Roswell Park Memorial Institute
(Graham et_ ad. , 1978). All four of these case-control studies relied
solely on frequency of consumption data for their assessments of
dietary intake.
A somewhat contradictory observation was reported by Hirayama
(1981), whose large-scale cohort study in Japan indicated that there
was a decrease In overall risk for cancer, including intestinal cancer,
in association with daily intake of meat.
Pancreatic Cancer
Lea (1967) examined the relationship between per capita intake of
foods and nutrients and cancer mortality resulting from up to 22 dif-
ferent types of neoplasms In each of 33 countries. One of the findings
was a strong direct correlation between intake of animal protein and
pancreatic cancer. This result was reproduced by Armstrong and Doll
(1975). No case-control or cohort studies have confirmed this asso-
ciation specifically; however, a study of pancreatic cancer cases and
controls in Japan (Ishii et_ auL. , 1968), based on responses to a mailed
questionnaire completed mostly by relatives of deceased cases, showed
an association of the disease with consumption of high-meat diets
by men. Hirayama (1977) reported a relative risk of 2.5 for dally meat
intake and pancreatic cancer incidence in Japan in a cohort of 265,118
subjects followed prospectively. Since meat is a major source of
protein in the diet, these findings offer tentative support for the
results of correlation studies.
6-4
Other Cancers
Armstrong and Doll (1975) found a strong correlation (correlation
coefficient = 0.8) between animal protein and the incidence of renal
cancer. However, in a subsequent case-control study, Armstrong et a.1.
(1976) found no clear association between renal cancer and consumption
frequencies for several foods containing animal protein (e.g., meat,
poultry, seafood, eggs, milk, and cheese).
The incidence of prostate cancer was significantly correlated
with consumption of total and animal protein in the study by Kolonel
et_ juU (1981), whereas mortality from, but not the incidence of,
prostate cancer was similarly correlated in the study by Armstrong and
Doll (1975). As noted in Chapter 5, Hirayama (1977) reported a sharp
increase in the intake of animal protein in Japan since 1950. During
this period, the incidence of prostate cancer in that country increased
correspondingly. The intake of meat, especially beef, has also been
correlated with mortality from prostate cancer (Armstrong and Doll,
1975; Howell, 1974).
The incidence of endometrial cancer has also been significantly
correlated with the intake of total protein (Armstrong and Doll, 1975;
Kolonel ot_ al. , 1981). This finding may simply reflect the high
correlation between the occurrence of endometrial cancer and breast
cancer, since the latter has also been associated with protein intake
(see Chapter 16). No case-control studies have been conducted to
examine this association.
EXPERIMENTAL EVIDENCE
There is much less literature on results of laboratory studies to
determine the relationship between cancer and dietary protein than has
been published for certain other nutrients (e.g., fat). However, an
inhibitory effect of selected amino acid deficiencies on tumor re-
sponses in laboratory animals was claimed as early as 1936 (Voegtlin
and Maver, 1936; Voegtlin and Thompson, 1936). During the subsequent
30 years, further studies concentrated primarily on the effect of
protein intake on experimental animal models. From the end of that
period to the present, attention became increasingly focused on
epidemiological studies.
In general, animals fed minimum amounts of protein required for
optimum growth have developed fewer tumors than comparable groups
fed 2 to 3 times the minimum requirements. Unfortunately, a number
of these earlier studies in animals are difficult to interpret for
several reasons: several factors were being varied at the same time
(Engel and Copeland, 1952a; Gilbert et_ al_. , 1958; Ross and Bras, 1965);
dietary levels of the carcinogen were different in the high and low
dietary protein groups (Harris, 1947); the total intake of food was
less for animals fed very high levels of protein (Gilbert et al., 1958;
6-5
Tannenbaum and Silverstone, 1949), and tumor growth is known to be
inhibited at lower food (and lower calorie) intake (Ross et^ aul. , 1970;
Tannenbaum, 1945a,b); and a high dietary level of fat, which may have a
tumor-enhancing effect, was present in the experimental diet (Ross and
Bras, 1973). Nonetheless, several of the earlier reports have pro-
vided useful information either because they were well controlled or
because they have been confirmed by other studies.
When considering the effect of dietary protein, it is important to
determine whether such an effect is specific for a particular amino
acid or is a general effect of protein. In a well-controlled study,
Silverstone and Tannenbaum (1951) reported that the spontaneous hepa-
tomas in C3H mice were less frequent (measured as percent of tumor-
bearing animals) in animals fed a 9% casein diet than in animals fed
18% or 45% casein diets. No significant difference in hepatomas was
observed for the latter two dietary groups. All three diets were
isocaloric and were fed to the mice at equivalent time intervals. In
additional experiments, this effect of protein was still marked when
the animals were fed diets that maintained their individual body
weights. Therefore, the investigators concluded that the effect of
protein was neither confounded with total food or caloric intake nor
related to the change in body weight. Adding 9% gelatin to the 9%
casein diet had little effect, whereas supplementation of that diet
with methionine and cystine (which is present in relatively low levels
in gelatin) increased the incidence of hepatomas to the level observed
for the mice fed the 18% casein diet. Therefore, it is the excess of
total protein or its adequacy as indicated by amino acid balance that
generates the increased tumor response. The addition of gelatin may
have resulted in extra total protein, but it did not compensate for the
growth-limiting sulfur amino acids. In one experiment, the effects of
an animal protein (casein) and a plant protein (isolated soy protein)
were compared, but no significant difference in tumor incidence was
noted (Carroll, 1975).
In earlier studies, Larsen and Heston (1945) found that cystine
added to a low casein diet given to Strain A male mice increased the
incidence of spontaneous pulmonary tumors from 28% to 54%. White and
Andervont (1943) observed that female C3H mice fed a cystine-def icient
casein diet exhibited no mammary gland tumors after 22 months, but
almost all the animals quickly developed tumors after their diets were
supplemented with cystine. Similarly, White and White (1944) observed
that mammary tumors occurred in only 25% of C3H mice fed a ly sine-
deficient gliadin diet but in nearly all of the mice when the diet was
supplemented with lysine. White jt.a3L (1947) later showed that only
cystine (bujfc not lysitie and tryptophan) was able to enhance the inci-
dence of 3^methylcholaisthreue-induced leukemia in casein-fed mice.
Thus, it appeal's that tumor enhancement by dietary protein occurs only
when there is amitK) fqid baia^e, suggesting that the effect is not due
to specific affiino aci.ds or t:o amino acid imbalance.
6-6
The effect of dietary protein on tumor incidence has been observed
both with and without pre treatment with chemical carcinogens. That is,
both "spontaneous" and chemically induced tumor responses may be influ-
enced by the level of dietary protein. These two kinds of responses
may not be distinct, since certain so-called spontaneous tumors may be
related to the prior ingestion of, or other exposure to, some unknown
initiator of carcinogenicity. For example, Newberne et al. (1966)
speculated that the occasional high incidence of liver tumors observed
in earlier studies may have been caused by aflatoxin contamination of
peanut meal fed to animals. Because it is now known that corn products
may be similarly contaminated, results of earlier studies using degermi-
nated corn grit diets should also be reevaluated, especially when an
unexpectedly high incidence of liver tumors has been observed, as in
the study of Engel and Copeland (1951). Similarly, the appearance of
some presumably spontaneous tumors may be due to the very potent
mutagens produced in heated or cooked foods (Sugimura, 1979).
Spontaneous Tumors
Ross and coworkers conducted extensive studies with large numbers
of rats in order to examine the effects of diet on mortality patterns
and lifespan (Ross and Bras, 1965, 1973; Ross t al. , 1970). They
focused on the influence of total food, caloric, and protein intake on
the appearance of a variety of tumors of unknown etiology. The total
incidence of various types of tumors was directly related to the intake
of calories, and the tumors appeared sooner when the caloric intake was
high (Ross and Bras, 1965).
Because the rats developed many types of tumors, the investigators
could not compare the effect of diet on specific types of tumors. The
highest number of any tumor type for any one diet was 11 the number of
f ibrosarcomas observed among the 210 animals in the 30% casein diet
group. The authors did note, however, that in two groups with identi-
cal caloric intake, there were more tumors in the group with the higher
protein intake. In these studies, only two of the four treatment
groups differed in only one dietary variable the ratio of casein to
sucrose. The diet with the higher ratio contained 30% casein; the one
with the lower ratio contained 8% casein. All other comparisons among
the treatment groups were confounded by two or more simultaneous
variables.
In a later study, Ross jet al . (1970) reported that the prevalence
of chromophobe adenomas of the anterior pituitary gland of male rats
was directly related to the level of dietary protein (10%, 22%, or 51%
casein). However, the tumor prevalence was 2;4% or less in each treat-
ment group, which would seem to invalidate any such conclusion* More-
over, the simple composition of the diet used in these studies is now
believed to be inadequate for studies of this type (Anonymous, 1977).
In their most recent study, Ross and Bras (1973) examined the effect of
6-7
10%, 22%, and 51% casein on the development of 58 types of tumors, none
of which involved more than 10% of the rats. They found that protein
had no effect on animals fed ad libitum, but that there were fewer
tumor-bearing animals in groups fed the lower protein diets if the
daily food intake was restricted to 6 g.
In addition to the studies by Silverstone and Tannenbaum (1951) and
White and Andervont (1943) described above, other reports that dietary
protein affects "spontaneous" tumors are those of Slonaker (1931),
White and White (1944), and Tannenbaum and Silverstone (1949). Although
Ross and Bras (1973) have interpreted the work of Slonaker (1931) as
having demonstrated an inverse relationship between protein intake and
tumor incidence (mammary gland and ovarian tumors in female rats and
skin tumors in male rats), further inspection of Slonaker 's report is
necessary. Slonaker (1931) stated that the diets contained 10%, 14%,
18%, 22%, and 26% protein, but he did not describe the composition of
the diets. Moreover, the numbers of tumor-bearing female animals were
5/20, 6/19, 5/17, 2/16, and 4/21 for the low to high protein groups,
and the author, without providing histological evidence, concluded that
the tumors "became cancer-like in appearance." For the males, skin
cancers were found in 1/22, 1/21, 1/17, 0/14, and 0/13 animals for the
low to high protein groups. Therefore, no firm conclusions can be
drawn concerning the association of protein intake with tumor appear-
ance.
Tannenbaum and Silverstone (1949) described a study in which diets
containing from 9% to 45% protein were fed ad libitum to an inbred
strain of mice. The incidence of spontaneous hepatomas in the animals
fed 9% casein diets was 11/44; in the animals fed 18% casein diets, it
was 28/46. However, no significant effect on either the incidence or
the average time of appearance was observed for the spontaneous mammary
tumors.
Chemically Induced Tumors
More studies have been conducted to determine the relationship of
dietary protein to chemically induced tumors than to spontaneous tumors.
When aflatoxin is fed with varying levels of protein, the inci-
dence of liver tumors is depressed at lower protein intakes. Madhavan
and Gopalan (1968) intubated weanling or young rats with aflatoxin
and then fed them either 5% or 20% casein diets for 1 year. They
observed that the incidence of hepatomas in the two groups was 0/12
and 15/30, respectively. These data summarize results from experi-
ments that used different protocols. Wells et al. (1976) fed diets
containing 8%, 22%, or 3QI casefn with 1.7 mg/kg aflatoxin B^
(AFBj_) to male weanling rats for 3 months, then the same diets
without AFB^ for as long as 1 year. Hepatomas were found in 0/16,
6/9, and 8/10 rats, respectively. This finding cotif irmed the results
6-8
of Madhavan and Gopalan (1968). Similarly, Temcharoen e a!l. (1978)
fed male rats an equal mixture of aflatoxin B^ and GI along with
diets containing either 5% casein or 20% casein for 33 weeks. They
found 4/47 hepatoma-bearing animals in the low protein group and 7/49
in the higher protein group, which is not in accord with their con-
clusion that "in animals fed a low-protein diet, aflatoxin induced
extensive . . . carcinogenic effects. 11 In contrast to the incidence
of hepatomas, the incidence of cystic lesions, cholangiof ibrosis,
cirrhosis, and hyperplastic nodules was higher among the animals fed
the low protein diets. This appears to be in agreement with the ob-
servations of other investigators that the effect of the level of
dietary protein on af la toxin-induced hepatotoxicity is the opposite of
its effect on aflatoxin-induced carcinogenesis (Madhavan and Gopalan,
1965, 1968).
The effect of dietary protein on the emergence of precancerous
lesions is not clear from these studies. Madhavan and Gopalan (1968)
reported fewer "preneoplastic lesions" in the animals fed the low pro-
tein diet. But Temcharoen et_ aJU (1978) observed more "hyperplastic
nodules" and other lesions in the low protein groups, suggesting that
their study might have been confounded by the simultaneous appearance
of toxic and carcinogenic lesions. Madhavan and Gopalan (1968)
administered aflatoxin early in their studies and then discontinued
further administration; Temcharoen et^ al. (1978) appeared to have
administered the toxin throughout the study, although this was not
explicitly stated. Part of the confusion about the association of low
protein intake and the hepatocarcinogenicity of aflatoxin results from
the use of the terms hepatotoxicity and hepatocarcinogenesls. These
effects are different, and have been used without definition in some
reports. Each of the studies cited above (i.e., Madhavan and Gopalan,
1968; Temcharoen e al. , 1978; Wells ert al. , 1976) is singularly
inconclusive, but collectively they support the hypothesis that a high
protein diet enhances aflatoxin-induced hepatocarcinogenesis.
Morris et al, (1948) found that more tumors of a greater variety
appeared in rats treated with N[-acetyl-2-aminofluorene (2-AAF) and fed
synthetic diets containing 18% and 24% casein than in similarly treated
animals fed diets containing 12% casein. Engel and Copeland (1952b)
observed that dietary protein did not affect 2-AAF-induced tumors in
rats fed ad libitum with diets containing 9% to 27% casein. There was,
however, a highly significant reduction in the incidence of mammary
tumors in rats fed diets containing 40% to 60% casein. When the 9% and
60% protein diets were pair-fed, i.e., fed to two matched groups, the
incidence of mammary tumors was 80% and 12%, respectively. Ad libitum
feeding of the 60% protein diet, however, overcame some of the inhibi-
tion (77% incidence), indicating inhibition of tumorigenesis by very
high protein diets can be overcome by increasing food intake. Harris
(1947) concluded that protein had no effect on carcinogmesis induced
either by 2-AAF or by aminofluorene (AF), which ^as applied to the
6-9
skin. In the 2-AAF-treated rats, reduction in the total incidence of
tumors from 65% to 45% in males and from 80% to 70% in females resulted
from a modest reduction in dietary casein from 20% to 13%. In animals
receiving the low protein diet, the incidence of liver tumors was de-
pressed from 50% to 30% in males and from 20% to in females.
Walters and Roe (1964) injected mice within 24 hours of birth with
9,10-dimethyl-l,2-benzanthracene (DMBA) and then fed them diets con-
taining either 25% or between 10% and 15% casein. The animals fed the
higher level of casein developed significantly more lung tumors. In
contrast, other reports showed that a reduction of the protein content
of the diet enhanced the formation of DMBA-induced hepatomas (Elson,
1958; Miller et_ cuL. , 1941; Silverstone, 1948) and mammary tumors
(Clinton et aT7,~979) in rats. Clinton e al. (1979) studied the
effect of dietary protein levels on the incidence of DMBA-induced mam-
mary tumors in rats and observed that the effect of protein depended on
whether the dietary treatment occurred before or after the administra-
tion of the carcinogen.
Topping and Visek (1976) studied the effect of dietary protein on
the induction of adenocarcinomas of the small and large intestines of
rats by 1,2-dimethylhydrazine. They observed that the tumors were
larger and more numerous in the rats fed diets containing 15% and 22.5%
protein than in those given 7.5% protein diets. Moreover, the 22.5%
protein diets also caused an earlier appearance of keratin-producing
papillomas of the sebaceous glands of the external ear.
Shay et al. (1964) studied the effect of dietary protein on tumori-
genesis induced by 3-methylcholanthrene. They observed an increase in
mammary adenocarcinomas in pretreated rats fed high levels of protein
(27% to 64% casein). In an earlier study, White et al. (1947) reported
that a high protein diet enhanced 3-methylcholantEFene-induced leukemia
in mice.
Extensive studies have been undertaken to determine the mechanism
by which dietary protein alters AFB^-induced tumorigenesis. A low
protein intake depresses the mixed-function oxygenase (Mgbodile and
Campbell, 1972) responsible for AFB^ metabolism as well as the
in vivo formation of AFB^-DNA covalent adducts (Preston et al.,
1976). Although Campbell (1979) suggested that modification of
metabolism was responsible for the effect of dietary protein on
tumorigenicity, more recent studies indicate that the effect of dietary
protein on events occurring after initiation may be more important.
For example, the development of Y-glutamyl transpeptidase hepatpcellu-
ular foci, which is an excellent early indicator of hepatocarcinogenesis
(Tsuda e a^. , 1980) , is greatly depressed in rats fed a 5% caseiti diet
compared to rats fed a 20% casein diet, both given after the adminis-
tration of AFB^ is completed (Appleton and Campbell, 1981). This
postinitiation effect of the low protein diet was even capable of pver-
coming the potential carcinbgenic effects of a higher AFB^-DNA l
6-10
level, which had been established by feeding high levels of protein
during AFBj administration.
Tumor Transplantation Studies
Low protein diets have also been associated with the general
inhibition of the growth of transplanted tumors. Haley and Williamson
(1960) implanted HAD-1 tumors into rats fed a diet with no protein and
rats fed a 20% casein control diet. They observed that the resultant
tumors were smaller in the no protein diet group. Earlier, Babson
(1954) had found that increasing dietary casein from to 18% increased
tumor growth rates in rats implanted either with the Sarcoma R-l tumor
or the Flexner-Jobling carcinosarcoma. According to Devik et al.
(1950), there was a prolonged inflammatory reaction to the Implantation
of the Walker carcinosarcoma 256 and incomplete connective tissue
encapsulation in animals fed 5% casein diets, compared to animals fed
20% casein diets.
White and Belkin (1945) studied the effect of low protein diets on
the "take" of implanted mammary carcinoma 15091a. Although the number
of takes was higher (16/31) in the protein-deficient group than in the
adequate dietary protein group (10/31), the growth rate at 3 weeks was
only 74% of the rate for the higher protein diet. These tumor implan-
tation studies were later summarized by White (1961).
The mechanism for the inhibition of tumor growth by low protein
diets is not known. Jose and Good (1973) have proposed that the cellu-
lar immune response may be involved. This response is enhanced through
a deficiency of blocking serum antibody production at low levels of
protein intake.
An Evaluation of the Data from Animal Studies
The relationship of dietary protein to the carcinogenic process
does not appear to be straightforward. Levels of protein ranging from
those somewhat below the minimum required for optimum growth (approxi-
mately 5% of the diet) up to those generally consumed by mammals (15%
to 20%) have been studied most extensively. In many studies in animals,
diets with low protein (near or below the requirement for optimum
growth) have generally been shown to suppress the carcinogenic process
and the subsequent growth and development of tumors. The only apparent
exception to this effect is the increase in DMBA-induced tumor yield in
animals fed low protein diets. Although there is generally a tumor-
enhancing effect from 20% to 25% dietary protein, higher levels appear
either to produce no further enhancement or, in fact, to inhibit tumor-
igenesis (Appleton and Campbell, 1981; Engel and Copeland, 1952b; Ross
and Bras, 1973; Ross et al. , 1970; Saxton et^ al. , 1948; Tannenbaum and
Silverstone, 1949; Topping and Visek, 1976; Wells e al. , 1976). It is
not clear whether the general inhibition or the absence of effect on
6-11
tumorigenesis at very high levels of dietary protein is due to a
reduced intake of food and total calories or whether It is due to other
adverse effects, e.g., renal toxicity due to high levels of protein.
SUMMARY
Epidemiological Evidence
Epidemiological studies have suggested possible associations
between high levels of dietary protein and increased risk of cancers
at a number of different sites. However, the literature on protein is
much more limited than the literature concerning fats and cancer. In
addition, because of the very high correlation between fat and protein
Intake In Western diets, and the more consistent and often stronger
association of these cancers with fat intake, it seems more likely
that dietary fat Is the more active component. Nevertheless, the evi-
dence does not completely preclude an independent effect of protein.
Experimental Evidence
In laboratory experiments, the relationship of dietary protein to
carcinogenesis appears to depend upon the level of protein intake. In
most studies, carcinogenesis was suppressed by diets containing levels
of protein at or below the minimum required for optimum growth.
Chemically induced carcinogenesis appears to be enhanced as protein
Intake is increased up to 2 or 3 times the normal requirement; however,
higher levels of protein begin to inhibit carcinogenesis. There Is
some evidence to suggest that protein may affect the initiation phase
of carcinogenesis and/or the subsequent growth and development of the
tumor.
CONCLUSION
Thus, evidence from both epidemiological and laboratory studies
suggests that protein Intake may be associated with an increased risk
of cancers of certain sites. Because of the relative pauqity of data
on protein compared to fat, ai*d the strong correlation between intakes
of fat and protein in the Western diet, the committee is unable to
arrive at a firm comclusi9n afrput an independent effect of protein.
6-12
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6-13
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6-14
Hems, G. 1978. The contributions of diet and childbearing to breast-
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child-bearing and diet in the United Kingdom. Br. J. Cancer
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Lea, A. J. 1967. Neoplasms and environmental factors. Ann. R.
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6-16
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6-17
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CHAPTER 7
CARBOHYDRATES
In contrast to lipids and protein, which are the other two macro-
nutrients in the diet, very little attention has been directed toward the
study of carbohydrate intake and the occurrence of cancer. The principal
carbohydrates in foods are sugars, starches, and cellulose. Evidence per-
taining to sugars and starches is evaluated in this chapter. The data on
cellulose are discussed under dietary fiber (Chapter 8).
EPIDEMIOLOGICAL EVIDENCE
There is little epidemiological evidence to support a role for
carbohydrates per se in the etiology of cancer. Fiber as a separate
dietary component is discussed in Chapter 8.
Armstrong and Doll (1975) correlated per capita intake of foods and
specific nutrients with cancer incidence and mortality in 23 and 32
countries, respectively. They found a significant direct correlation
between sugar intake and pancreatic cancer mortality (but not incidence)
in women only. They also reported a weak association between liver
cancer incidence and the intake of potatoes a starch-rich vegetable.
There are no reports of case-control studies that support either of these
findings.
Hems (1978) reported a study concerning the relationship of diet and
breast cancer among women in 4.1 countries. He found that a high intake
of refined sugar was one of the dietary components associated with
increased incidence of breast cancet. This finding is consistent with
findings in laboratory experiments. However, in an earlier study, Hems
and Stuart (1975) found an inverse relationship between breast cancer
incidence and another dietary carbohydrate- starch.
Hakama and Saxen (1967) analyzed age- and seX-ad justed mortality
rates for stomach cancer in 16 countries. They found a strong corre-
lation (r = 0.75) ttith the per capita intake of cereal used as flour
from 1934 to 1938. In a study of per capita food intake and cancer risk
in 37 countries, Drasar and! Irving (1973) observed a direct correlation
between breast cancer and the intake of simple sugars.
In a case-control study of gastric cancer, Modan et_ al. (1974)
observed that high starch foods were consumed more frequently by cases
than by controls. This finding has not been reported in other studies of
gastric cancer. De Jong e al . (1974) studied cases of esophageal cancer
and hospital controls in Singapore. Among their findings was a direct
association between consumption of bread and potatoes (major sources <?f
7-2
dietary carbohydrates) and risk of esophageal cancer* Once again, other
investigators who have studied cancer at this site have not observed a
similar association.
EXPERIMENTAL EVIDENCE
There have also been only a few laboratory experiments to study the
relationship between carbohydrates and cancer. These studies have gen-
erally been conducted by varying the concentration of the test substance,
e.g., starch, sucrose, dextrin, or glucose, in a basal diet. Often,
little attention has been given to the differences in the caloric content
of the control and experimental diets. Furthermore, the variation in
carbohydrate content, resulting from attempts to "balance" diets on a
weight basis, has generally been disregarded. A few recent studies have
focused on the effects of long-term carbohydrate feeding on tumorigenesis
Sucrose
The effects of long-term (more than 1 year) feeding or systemic
administration of sucrose on spontaneously occurring tumors have been
studied in both mice and rats. Roe e aJL . (1970) fed sucrose to mice at
10% by weight of the diet (^15 g/kg body weight [bw]), and Friedman e
al. (1972) fed rats sucrose at 77% by weight of the diet (^40 g/kg bw),
In neither study was there an increase in the incidence of tumors.
Intraperitoneal or subcutaneous injections of sucrose given over vari-
ous lengths of time (Nonaka, 1938; Takizawa, 1939; Zarattini, 1940) or
systemic administration of 20% sucrose twice weekly for 2 years produced
no evidence of carcinogenesis in either rats or mice (Hueper, 1965).
Hunter et ad. (1978a) fed CFLP mice 20% sucrose in the diet for 2
years. The females, but not the males, exhibited a higher incidence of
hepatocellular tumors. Parallel feeding studies by the same investiga-
tors in which 20% sucrose diets were fed to male and female Sprague-
Dawley (CD) rats for up to 1 year and to male and female beagle dogs for
up to 2 years did not provide any evidence that sucrose contributed to
tumorigenesis. This study has not been repeated.
Hoehn and Carroll (1978) evaluated the effect of dietary carbohy-
drates on chemically induced tumors in rats. After breast tumors were
induced with 7,12-dimethylbenz [a.] anthracene, rats were fed diets con-
taining either refined sugar or complex starches. Significantly more
breast tumors were observed in rats fed refined sugar than in those fed
starch.
Much more experimental work is required before ^conclusion can be
drawn about the relationship between sucrose aqd carcinogeiiesis.
7-3
Lactose
Gershoff and McGandy (1981) studied the interaction of dietary lactose
(49%) or sucrose (43%-55% total weight) with vitamin A deficiency in the
production of primary urinary bladder calculi in male Charles River
rats. A small percentage of rats fed lactose in a diet with sufficient
vitamin A developed vesicle stones. Approximately 60% of the rats fed
lactose in vitamin-A-deficient diets developed bladder calculi. The
bladder walls in most of the affected rats were grossly hypertrophic and
had focal areas of transitional cell hyperplasia. Histological changes
consistent with grade I to II transitional cell carcinomas were observed
in approximately 30% of the stone-containing bladders. It was not possi-
ble to discern whether the deficiency of vitamin A contributed directly
to bladder tumors or indirectly via stone formation and subsequent physi-
cal irritation of the bladder. Sucrose-fed rats with or without super-
imposed vitamin A deficiency did not exhibit calculi or histological
changes of the bladder. The authors remarked that this was the first
study to demonstrate the production of tumors by diet without an exog-
enous source of a carcinogen in animals not genetically predisposed to
tumor formation.
Glucose
A preliminary report by Ingram and Castleden (1981) implicated
dietary glucose in the development of carcinogen-induced tumors in the
large bowel. In this study, male Wistar rats were fed Milne's Standard
Laboratory Diet and given drinking water ad libitum either with or
without 1.6% glucose. Both groups were injected subcutaneously with
1, 2-dimethylhydrazlne to induce bowel tumors. There were no differences
in the number of small bowel tumors observed in the two groups; however,
the rats given the glucose solution developed approximately twice the
number of large bowel tumors observed in those given the drinking water
alone. These results are difficult to interpret because approximately
35% of the Milne Standard Laboratory Diet is composed of carbohydrates,
and this diet was fed to both groups of animals. The contribution of
this diet to blood glucose levels is considerably greater than that
supplied by the 1.6% glucose-water drinking solution. Thus, there Is a
possibility that the observed results were 1 an indirect effect of the
glucose-water solution rather than a direct effect of glucose.
Xylitol
Xylitol is present in many natural foods (Washlittl et_ j^U , 1973).
Its sweetness is approximately equal to that of sucrose*
In a 2-year feeding study, CFLP male and female mice were fed 0, 2%,
10%, or 20% xyjitol in the diet for as long as 106 Sweeks (Hunter et al.,
7-4
1978b). In the mice fed the 10% or 20% xylitol diets, there was a re-
duction in spontaneous hepatocellular tumors in the males, but not in the
females. However, the males in these dietary groups had more crystalline
bladder calculi and an associated increase in hyperplasia, metaplasia,
and neoplasia of the transitional epithelium of the bladder than did the
females fed similar diets, the control mice, or the mice fed 2% xylitol.
Sprague-Dawley CD male and female rats were fed 2%, 5%, 10%, or 20%
xylitol in the diet for 26 weeks without evidence of increased renal
calculi or hepatocellular abnormalities at autopsy. However, the inci-
dence of adrenal medullary hyperplasia was greater in rats fed 5%, 10%,
or 20% xylitol than in the controls (Hunter et^ a^. , 1978b). In male and
female beagle dogs fed 10% or 20% xylitol in their diets for 52 weeks,
the single remarkable pathologic change was an increased liver weight at
autopsy. This slight hepatomegaly was associated with hepatocyte en-
largement and altered hepatocyte appearance in the periportal areas of
the animals.
The quantity of xylitol in the 20% diet approaches the LD^g for
xylitol in mice (Kieckebuch t^ al . , 1961). In rats, ingestion of 20%
xylitol may exceed the maximum metabolic turnover rate as calculated
from rates observed in humans (Biokel and Halmagyi, 1976).
SUMMARY
Epidemiological Evidence
The evidence concerning the role of carbohydrates in the development
of cancer in humans is extremely limited. In one study, the intake of
sugar was correlated with increased mortality from pancreatic cancer in
women only, and the intake of potatoes was correlated with increased
mortality from liver cancer in both sexes. In other studies, a high
intake of refined sugar and a low intake of starch have been associated
with an increased incidence of breast cancer. Frequent consumption of
starch has been associated with a high incidence of gastric cancer in one
case-control study and with esophageal cancer in another. However, the
evidence is insufficient to permit any firm conclusions to be drawn.
Experimental Evidence
The data from the few laboratory experiments designed to study the
role of carbohydrates in carcinogenesis are difficult to interpret
because of generally poor experimental designs and because there is
uncertainty about the actual carbohydrate content of the foods used in
the test diets.
A few recent studies suggest that dietary lactose combined with
vitamin A deprivation and long-term feeding of high levels of sucrose and
7-5
xylitol may contribute to carcinogens sis. These observations require
further study.
CONCLUSION
Thus, the evidence from both epidemiological and laboratory studies
is too sparse to suggest a direct role for carbohydrates (possibly
exclusive of fiber) in carcinogenesis. However, excessive carbohydrate
consumption contributes to caloric excess, which in turn has been im-
plicated as a modifier of carcinogenesis.
7-6
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Drasar, B., and D. Irving. 1973. Environmental factors and cancer of
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Gershoff, S. N., and R. B. McGandy. 1981. The effects of vitamin A-
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tumors in rats. Am. J. Clin. Nutr. 34:483-489.
>
Hakama, M., and E. A. Saxen. 1967. Cereal consumption and gastric
cancer. Int. J. Cancer 2:265-268.
Hems, G. 1978. The contribution of diet and childbearing to breast-
cancer rates. Br. J. Cancer 37:974-982.
Hems, G. , and A. Stuart. 1975. Breast cancer rates in populations
of single women. Br. J. Cancer 31:118-123.
Hoehn, S. K. , and K. K. Carroll. 1978. Effects of dietary carbohy-
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dimethylbenz(a.)anthracene. Nutr. Cancer 1:27-30.
Hueper, W. C. 1965. Are sugars carcinogens? An experimental study.
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Hunter, B., C. Graham, R. Heywood, D. E. Prentice, F. J. C. Roe, and
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7-7
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mentally induced colorectal cancer: A preliminary report. Nutr.
Cancer 2:150-152.
Kieckebuch, W., W. Gzeim, and K. Lang. 1961. [In German.] Die
Verwertbarkeit von Xylit als Nahrungskohlenhydrat und seine
VertrMglichkeit. Kiln. Wochenschr. 39:447-448.
Modan, B., F. Lubin, V. Barrell, R. A. Greenberg, M. Modan, and S.
Graham. 1974. The role of starches in the etiology of gastric
cancer. Cancer 34:2087-2092.
Nonaka, T. 1938. [In Japanese; English Title.] The occurrence of sub-
cutaneous sarcomas in the rat after repeated injections of glucose
solution. Gann 32:234-235.
Roe, F. J. C., L. S. Levy, and R. L. Carter. 1970. Feeding studies on
sodium cyclamate, saccharin and sucrose for carcinogenic and tumour-
promoting activity. Food Cosmet. Toxicol. 8:135-145.
Takizawa, N. 1939. [In Japanese; German Title.] Uber die Erzeugung
des Maussarkoms durch die subcutane Injektion der konzentrierten
Zuckerlb'sung. (II. Mittellung.) Gann 33:193-195.
Washiittl, J., D. Reiderer, and E. Bancher. 1973. A qualitative and
quantitative study of sugar-alcohols in several foods. J. Food
Sci. 38:1262-1263.
Zarattini, A. 1940. [In Italian.] Sulla produzione sperimentale del
sarcoma nei ratti mediante somministrazione paraenterale di glucosio.
Tumor i 26:77-84.
CHAPTER 8
DIETARY FIBER
Recently, attention has been directed toward the physiological
significance of dietary fiber, which generally includes indigestible
carbohydrates and carbohydrate-like components of food such as cellulose,
lignin, hemicelluloses, pentosans, gums, and pectins. The principal
characteristic of these indigestible substances is their provision of
bulk in the diet. The major categories of foods that provide dietary
fiber are vegetables, fruits, and whole grain cereals.
Because of the complex composition of dietary fiber, the physio-
logical functions and metabolic activity of its individual components
have not been adequately studied. Most earlier analyses focused on the
intake of so-called "crude fiber. 11 Therefore, they generally under-
estimated the fiber content since crude fiber only determines cellulose
and lignin. Consequently, early reports provided incomplete data on the
amount and type of fiber consumed.
During the past few decades, the consumption of dietary fiber has
decreased in many parts of the Western world (National Academy of
Sciences, 1980). On the basis of observations concerning the rela-
tionship of diet and the incidence of disease, Burkitt and Trowell
(1975) hypothesized that many chronic diseases including cancer are
associated with a low intake of dietary fiber.
EPIDEMIQLOGICAL EVIDENCE
The epidemiological data on fiber are related primarily to Its
possible role in protection against large bowel cancer. Several
different mechanisms have been proposed for this protective effect:
Fiber can dilute carcinogens present in the large bowel; it can de-
crease transit time, thereby decreasing contact time between carcinogen
and tissue; it can affect the production of putative carcinogens or
procarcinogens in the stool such as the bile acids; or, by Influencing
the composition and metabolic activity of the fecal flora, It can alter
the spectrum of fecal bile acids and their derivatives that are present
in the stool. Most data on the fiber content of foods are incomplete,
because they pertain only to crude fiber. Since any effect associated
with dietary fiber m^y be restricted to selected components, epldemlo-
logical studies of tletaty fiber ^rill have limited v^lue until detailed
information on eadh of Its Constituents becomes available.
Attempts to correlate the fiber content of diets with colorectal
cancer risk have yielded mixed results. Malhotra (1977) suggested
the differences in colon cancer incidence among northern and southern
8-2
populations in India might be explained by the high levels of roughage,
cellulose, and vegetable fiber in the northern Indian diet and the very
low levels in the southern Indian diet. There was a virtual absence of
the disease in the Punjabis from the north. He also found that vegeta-
ble fibers were abundant in the stools of Indians from the north, but
completely absent in samples obtained from inhabitants of the southern
regions. MacLennan t al. (1978) observed similar differences after
comparing the diets of adult men from Copenhagen, Denmark (high risk
group for colon cancer) and from Kuopio, Finland (low risk group). The
Danes consumed less fiber and their stools weighed less than those of the
Finns, These findings lend support to the hypothesis that dietary fiber
plays a protective role in carcinogenesis. Bingham et_ al_. (1979) calcu-
lated the average fiber intake by populations in different regions of
Great Britain. They found no significant correlation between total fiber
intake and corresponding mortality rates for colon and rectal cancers.
However, the mean intakes of the pentosan fraction of total dietary fiber
and of vegetables other than potatoes were inversely correlated with
mortality from colon cancer. This finding suggested the importance of
examining the specific components of fiber rather than crude or total
fiber in studies of large bowel cancer.
Other correlation analyses have not supported the hypothesis that
fiber intake is inversely associated with the risk of colon cancer. Liu
:L' (1979) examined mortality from colon cancer in 20 industralized
countries between 1967 and 1973 and compared the rates to per capita food
intake for these same areas from 1954 to 1965. Although fiber intake was
inversely correlated with colon cancer mortality, this relationship was
no longer significant in a partial correlation analysis controlling for
cholesterol intake. The authors concluded that cholesterol, not fiber,
was an important risk factor for colon cancer. In other studies, Drasar
and Irving (1973) failed to find a correlation between colon cancer in-
cidence in 37 countries and per capita intake of various fiber- containing
foods, and Lyon and Sorenson (1978) found little difference in fiber
intake between the population of Utah (low risk) and the population of
the United States as a whole.
In a number of case-control studies, investigators have attempted to
examine the relationship between dietary fiber and risk of large bowel
cancer, again with inconsistent results. Modan t_ al . (1975) assessed
the frequency with which certain food items were consumed by colon and
rectal cancer cases and both hospital and neighborhood controls. They
found that the consumption of high-fiber foods by colon cancer cases was
significantly lower than that of both groups of controls, but there was
no such difference between rectal cancer cases and controls. Using a
similar approach, Bjelke (1978) observed that the consumption of dietary
fiber by colorectal cancer cases was lower than that of controls in
parallel studies conducted in Minnesota and Norway.
Dales et_ al_. (1978) studied cases of colorectal cancer in U.S.
blacks. Controls were selected from two hospitals and a multiphasic
8-3
health check-up clinic. By assessing the frequency of consumption of
selected food items, they found that the cases consumed fewer fiber-
containing foods than did the controls, and that there was a consistent
dose-response relationship. Significantly more cases than controls
reported the consumption of a diet that was high in saturated fat but
low in fiber.
In a case-control study of diet and colorectal cancer in Canada, Jain
e_t_ al. (1980) attempted to compute consumption of dietary fiber based on
the actual fiber content of food rather than on a simple grouping of food
items as other investigators had done. They found an elevated risk asso-
ciated with increased consumption of calories, total fat, total protein,
saturated fat, oleic acid, and cholesterol, but no association with the
consumption of crude fiber, vitamin C, or linoleic acid. Unfortunately,
data on the specific components of fiber were not available for their
analysis.
An inverse association between fiber consumption and large bowel
cancer was reported by Martinez et_ al_. (1979), who conducted a case-
control study in Puerto Rico. Based on frequency-of-consumption dietary
histories, they found higher consumption of fiber and total residue in
cases than in controls. They provided no explanation for this unusual
finding, which, however, is consistent with the observation of Hill et
al (1979) that the highest socioeconomic group studied in Hong Kong had
the highest incidence of colon cancer and a high intake of fiber and
calories, whereas the middle and lowest socioeconomic groups had corre-
spondingly lower incidence rates and intakes.
Glober et ail. (1974, 1977), compared bowel transit-times in men
from three different populations: Japanese in Japan (low risk for colon
cancer), Japanese in Hawaii (high risk for colon cancer), and Caucasians
in Hawaii (also high risk for colon cancer) . They found that bowel
transit-times were similar in both Japanese populations, and were shorter
than in the Caucasians. Mean stool weight, however, was similar in the
two high-risk populations and was notably less than that for the Japanese
in Japan. Thus, their data did not support the hypothesis that dietary
fiber protects against colon cancer by decreasing transit time in the
bowel, thereby decreasing the contact time between carcinogens and
tissues.
Dietary fiber can also affect the amount of bile acids excreted into
the lumen of the intestine. However, since dietary fat influences bile
acid excretion as well, the relative effects of both of these dietary
components need further study. Studies of the composition of bile acids
in the feces of humans are reviewed in Chapter 5.
EXPERIMENTAL EVIDENCE
A variety of chemical carcinogens cause colon cancer in rats. Anoiig
these are 1,2-dimethylhydrazine (DMH), azoxymethane (AOM), methyl-
azoxymethanol (MAM) acetate, 3,2 f -dimethyl-4-aminobiphenyl (DAB), and
8-4
nitrosomethylurea (NMU). Colon cancer can be induced in these labora-
tory animals by parenteral administration of DMH, AOM, MAM, and DAB; by
feeding DMH; and by intrarectal instillation of NMU. Bran protects rats
against DMH-induced colon cancer, regardless of whether the carcinogen is
administered orally or subcutaneously (Barbolt and Abraham, 1978; Chen et
al. , 1978; Wilson aJ. , 1977). However, it has no effect on the
incidence or number of tumors in the duodenum or cecum. Cellulose has
been found to protect rats against DMH-induced tumors (Freeman et al.,
1978, 1980), but pectin does not (Freeman et_ aJ^. , 1980). Cellulose does
not appear to protect against tumors induced by AOM or NMU (Ward et al.
1973; Watanabe ejt al. , 1978).
Fleiszer et al. (1980) have studied the effects of different levels
of fiber on DMH-induced colon cancer in rats. Four diets were used:
very high fiber (28%) supplied as bran cereal; high fiber (15%) supplied
as a special rat chow; low fiber (5%) supplied as standard rat chow; and
a fiber-free, semipurified diet. Fewer cancers occurred in the rats fed
the very high fiber and high fiber diets, than in those given the low
fiber diet. Because the basal diet for the fiber-free group was con-
siderably different, the response of these animals cannot be reasonably
compared with those of the other animals.
Although components of dietary fiber generally appear to exert a
protective effect against DMH-induced carcinogenesis, Glauert et al.
(1981) recently reported that dietary agar (a fiber-rich component of
the diet) enhanced DMH-induced colon cancer in mice.
The effects of dietary fiber have been compared in rats treated with
AOM or NMU (Watanabe et^ al. , 1979). The substances tested were alfalfa,
pectin, and wheat bran fed as 15% of a diet that also contained 5% cell-
ulose. When the carcinogen was given parent erally, pectin exerted a
protective effect but alfalfa and bran were ineffective. When the car-
cinogen was given by intrarectal instillation, alfalfa enhanced carcin-
ogenesis, but pectin and bran were not protective.
Alfalfa has a relatively strong ability to bind bile acids (Story and
Kritchevsky, 1976). Cassidy et_ a_l. (1981) demonstrated that substances
with this binding capacity disrupt the topography of the colonic mucosa.
The denuded epithelium would then be susceptible to the action of a
locally administered carcinogen.
Although some data suggest that some types of fiber (e.g., bran and
cellulose) can protect rats from the action of certain chemical carcino-
gens, the collated data from different experiments are difficult to com-
pare or interpret, primarily because of the lack of uniform experimental
protocols. The strains of rats, their diets, age, the carcinogens used,
and routes of administration all differ. The animal model is useful to
study the effects of fiber on carcinogenesis in the large bowel, but the
lack of standardization must be borne in mind when assessing or comparing
data. , ... ; -;, : ,, ,. , }' ,:, . ., ,.. ;.
8-5
SUMMARY
Epidemiological Evidence
Both correlation and case-control studies have yielded results that
either support or contradict the hypothesis that dietary fiber protects
against colorectal cancer. In both types of studies, most analyses have
been based on total fiber consumption estimated by grouping foods (such
as fruits, vegetables, and cereals) according to their fiber content.
However, in the only case-control study and the only correlation study in
which the total fiber consumption was quantified rather than estimated
from the fiber-rich foods in the diet, no association was found between
total fiber consumption and the risk of colon cancer. Thus, the epidem-
iological evidence suggesting an inverse relationship between total fiber
intake and the occurrence of colon cancer is not yet compelling.
In the only study in which the effects of individual components of
fiber were assessed, there was an inverse correlation between the inci-
dence of colon cancer and the consumption of the pentosan fraction of
fiber (found in whole wheat products). Thus, it seems likely that
further epidemiological study of fiber will be productive only if the
relationship of cancer to specific components of fiber can be analyzed.
Experimental Evidence
A few laboratory studies have also shown that some types of high
fiber ingredients (e.g., cellulose and bran) depress the tumorigenicity
of certain chemical carcinogens. However, the data are inconsistent
especially with respect to the type of fiber or specific chemical car-
cinogen. Moreover, they are difficult to equate with the results of
epidemiological studies because most laboratory experiments have examined
specific fibers or their individual components, whereas most epidemio-
logical studies have focused on fiber-containing foods whose exact compo-
sition has not been determined* Further information is needed on the
basic chemistry and biological effects of fiber and its components to
pursue experimental studies that will pro.duce meaningful results.
CONCLUSION
The committee found no conclusive evidence to indicate that dietary
fiber (such as that pte sent in fruits, vegetables, grains, and cereals)
exerts a protective effect against colorectal cancer in humans. Both
epidemiological and laboratory reports suggest that if there is such an
effect, specific components Of fiber* rather than total dietary fiber,
are more 1 "likely' to; ;<fce
8-6
REFERENCES
Barbolt, T. A., and R. Abraham. 1978. The effect of bran on dimethyl-
hydra zine-induced colon carcinogenesis in the rat. Proc. Soc. Exp.
Biol. Med. 157:656-659.
Bingham, S., D. R. R. Williams, T. J. Cole, and W. P. T. James. 1979.
Dietary fibre and regional large-bowel cancer mortality in Britain.
Br. J. Cancer 40:456-463.
Bjelke, E. 1978. Dietary factors and the epidemiology of cancer of the
stomach and large bowel. Aktuel. Ernaehrungsmed. Klin. Prax.
Suppl. 2:10-17.
Burkitt, D. P., and H. C. Trowell. 1975. Refined Carbohydrate Foods
and Disease. Some Implications of Dietary Fibre. Academic Press,
London, New York, and San Francisco. 356 pp.
Cassidy, M. M. , F. G. Lightfoot, L. E. Grau, J. A. Story, D. Kritchevsky,
and G. V. Vahouny. 1981. Effect of chronic intake of dietary fibers
on the ultrastructural topography of rat jejunum and colon: A
scanning electron microscopy study. Am. J. Clin. Nutr. 34:218-228.
Chen, W.-F., A. S. Patchefsky, and H. S. Goldsmith. 1978. Colonic
protection from dimethylhydrazine by a high fiber diet. Surg.
Gynecol. Obstet. 147:503-506.
Dales, L. G., G. D. Friedman, H. K. Ury, S. Grossman, and S. R.
Williams. 1978. A case-control study of relationships of diet and
other traits to colorectal cancer in American blacks. Am. J.
Epidemiol. 109:132-144.
Drasar, B. S., and D. Irving. 1973. Environmental factors and cancer
of the colon and breast. Br. J. Cancer 27:167-172.
Fleiszer, D. M., D. Murray, G. K. Richards, and R. A. Brown. 1980.
Effects of diet on chemically induced bowel cancer. Can. J. Surg.
23:67-73.
Freeman, H. J., G. A. Spiller, and Y. S. Kim. 1978. A double-blind
study on the effect of purified cellulose dietary fiber on 1,2-
dimethylhydrazine-induced rat colonic neoplasia. Cancer Res.
38:2912-2917.
Freeman, H. J., G. A. Spiller, and Y. S. Kim. 1980. A double-blind
study on the effects of differing purified cellulose and pectin
8-7
fiber diets on 1,2-dimethylhydrazine-induced rat colonic neoplasia.
Cancer Res. 40:2661-2665.
Glauert, H. P., M. R. Bennink, and C. H. Sander. 1981. Enhancement
of 1,2-dimethylhydrazine-induced colon carcinogenesis in mice by
dietary agar. Food Cosmet. Toxicol. 19:281-286.
Glober, G. A., K. L. Klein, J. 0. Moore, and B. C. Abba. 1974. Bowel
transit-times in two populations experiencing similar colon-cancer
risks. Lancet 2:80-81.
Glober, G. A., A. Nomura, S. Kamiyama, A. Shimada, and B. C. Abba.
1977. Bowel transit-time and stool weight in populations with
different colon-cancer risks. Lancet 2:110-111.
Hill, M., R. MacLennan, and K. Newcombe. 1979. Letter to the Editor:
Diet and large-bowel cancer in three socioeconomic groups in Hong
Kong. Lancet 1:436.
Jain, M., G. M. Cook, F. G. Davis, M. G. Grace, G. R. Howe, and A. B.
Miller. 1980. A case-control study of diet and colo-rectal
cancer. Int. J. Cancer 26:757-768.
Liu, K. , J. Stamler, D. Moss, D. Garside, V. Persky, and I. Soltero.
1979. Dietary cholesterol, fat, and fibre, and colon-cancer
mortality. Lancet 2:782-785.
Lyon, J. L., and A. W. Sorenson. 1978. Colon cancer in a low-risk
population. Am. J. Clin. Nutr. 31:8227-8230.
MacLennan, R., 0. M. Jensen, J. Mosbech, and H. Vuori. 1978. Diet,
transit time, stool weight, and colon cancer in two Scandinavian
populations. Am. J. Clin. Nutr. 31 :S239-S242.
Malhotra, S. L. 1977. Dietary factors in a study of cancer colon
from cancer registry, with special reference to the role of saliva,
milk and fermented milk products and vegetable fibre. Med.
Hypotheses 3:122-126.
Martinez, I., R. Torres, Z. Frias, J. R. Colon, and M. Fernandez.
1979. Factors associated with adenocarcinomas of the large bowel
in Puerto Rico. Pp. 45-52 in J. M. Birch, ed. Advances in Medical
Oncology, Research and Education. Volume 3: Epidemiology.
Pergamon Press, Oxford, New York, Toronto, Sydney, Paris, and
Frankfurt .
Modan, B. , V. Barell, F. Lubin, M. Modan, R. A. Greenberg, and
S. Graham. 1975. Low-fiber intake as an etiologic factor in
cancer of the colon. J. Natl. Cancer Inst. 55:15-18.
National Academy of Sciences. 1980. Recommended Dietary Allowances,
9th Edition. Committee on Dietary Allowances, Food and Nutrition
Board, National Academy of Sciences, Washington, D.C. 187 pp.
Story, J. A., and D. Kritchevsky. 1976. Comparison of the binding
of various bile acids and bile salts in vitro by several types of
fiber. J. Nutr. 106:1292-1294.
Ward, J. M. , R. S. Yamamoto, and J. H. Weisburger. 1973. Cellulose
dietary bulk and azoxymethane-induced intestinal cancer. J. Natl.
Cancer Inst. 51:713-715.
Watanabe, K. , B. S. Reddy, C. Q. Wong, and J. H. Weisburger. 1978.
Effect of dietary undegraded carrageenin on colon carcinogenesis in
F344 rats treated with azoxymethane or methylnitrosourea. Cancer
Res. 38:4427-4430.
Watanabe, K. , B. S. Reddy, J. H. Weisburger, and D. Kritchevsky. 1979.
Effect of dietary alfalfa, pectin, and wheat bran on azoxymethane-
or methylnitrosourea-induced colon carcinogenesis in F344 rats. J.
Natl. Cancer Inst. 63:141-145.
Wilson, R. B., D. P. Hutcheson, and L. Wideman. 1977. Dimethyl-
hydrazine-induced colon tumors in rats fed diets containing beef
fat or corn oil with and without wheat bran. Am. J. Clin. Nutr.
30:176-181.
CHAPTER 9
VITAMINS
In recent years, there has been considerable interest in the role
of vitamins A, C, and E in the genesis and prevention of cancer. In
contrast, little attention has been paid to the B vitamins and others
such as vitamin K. The evidence concerning vitamins A, C, E, and
selected B vitamins is discussed below.
VITAMIN A
Of the entire collection of chemically diverse substances classi-
fied as vitamins, those subsumed under the general term "vitamin A" are
of the greatest current interest in terms of their possible association
with the process of carcinogenesis. The only well-understood function
of vitamin A is its role in the visual cycle. The involvement of this
vitamin in cell differentiation, although less well documented, pro-
vides a rational basis for examining its relationship to cancer.
Ingested vitamin A is absorbed in the bloodstream and stored in the
liver, and can reach toxic levels if large amounts are consumed. Blood
levels of vitamin A are regulated by a feedback mechanism, but they do
not usually reflect the amounts consumed in the diet or stored in the
liver.
Epidemiological Evidence
The impact of vitamin A on carcinogenesis is of considerable
interest. Several epidemiological investigations, mostly case-control
studies, have indicated an inverse relationship between "vitamin A 11
intake and a variety of cancers. With few exceptions, the estimates
of vitamin A were based on frequency of ingestion of a group of foods
(e.g., green and yellow vegetables) known to be rich in $-carotene (a
provitamin that may be enzymatically converted to vitamin A in vivo)
and a few foods such as whole milk and liver containing preformed
retinol (vitamin A). Thus, to a large extent, these studies have
measured indirect indices of 6-caroterie intake. In this discussion the
term vitamin A will also be used to include 3-carotene, since the two
components are not distinguished in most of the reports.
Lung. Bjelke (1975) was one of the first investigators to report
.epidemiological data suggesting that vitamin A plays a protective role
against cancer. Using frequency data, collected by a questionnaire
9-2
mailed to a cohort of Norwegian men, he derived a vitamin A index based
on limited sources of the vitamin. He observed lower values for lung
cancer cases than for controls after controlling for cigarette smoking.
MacLennan et al* (1977) found an inverse association between consumption
of green, leafy vegetables rich in "vitamin A" and lung cancer in a
case-control study among Chinese females in Singapore.
In a case-control study conducted by Gregor ejt^ JL!. (1980), hospital
outpatients, mostly from a rheumatology clinic, were used as controls.
These investigators found that significantly less vitamin A had been
consumed by male lung cancer cases than by controls, mainly because
cases had consumed fewer vitamin A supplements and less liver. The few
female cases had a different proportional distribution of tumor cell
type than the males and showed an opposite (direct) overall association
with vitamin A intake, although they also consumed fewer vitamin A
supplements than the controls.
The use of vitamin A supplements was inversely associated with
cancer, including lung cancer, in men (but not women) in a case-control
study reported by Smith and Jick (1978). Mettlin e_t al. (1979) reported
results of a case-control study in which an index of vitamin A consump-
tion, based on frequency of consumption of a group of food items, was
inversely associated with lung cancer in males, after controlling for
cigarette smoking. In 28 patients with bronchial carcinoma, plasma
levels of vitamin A were lower than those in a small group of controls
(Basu et a,!., 1976; Sakula, 1976).
Shekelle et_ al. (1981) reported the findings of a 19-year follow-
up study of 1,954 men in Chicago. Lung cancer incidence was inversely
associated with carotene intake both with and without adjustment for
cigarette smoking. There was no significant association of lung cancer
with the intake of preformed vitamin A.
Larynx. Graham et_ al. (1981) studied male cases of laryngeal can-
cer and controls. After controlling for cigarette smoking and alcohol
consumption, they found an inverse relationship (with a dose-response
gradient) between cancer risk and indices of both vitamins A and C in-
take based on frequency of consumption of selected foods. They reported
similar results for vegetable consumption in general, but not for cru-
ciferous vegetables in particular.
Bladder. In a case-control study designed like the one conducted
on lung cancer, Mettlin et^ al. (1979) reported a similar inverse asso-
ciation of a vitamin A consumption index with bladder cancer, after
controlling for coffee consumption, smoking, and occupational exposure.
Esophagus. Wynder and Bross (1961) reported that frequencies of
consumption of milk, and of green and yellow vegetables (sources of
vitamin A and g -carotene, respectively) were lower for esophageal
cancer cases than for controls. Mettlin et al. (1981) reported a
9-3
similar inverse association and a dose-response gradient for frequency
of consumption of fruits and vegetables in a study of male cases and
controls, after controlling for cigarette smoking and alcohol consump-
tion. Although they also found an inverse relationship for an index
of vitamin A consumption based on selected foods, there was an even
stronger inverse relationship for an index of vitamin C consumption*
Also consistent with these findings were observations of populations in
the Caspian littoral of Iran (a region of particularly high esophageal
cancer incidence) indicating that consumption of green vegetables and
fresh fruit and estimated vitamin A and C intake in high risk areas
were lower than in areas of low risk (Horaozdiari et^ al 1975; Joint
Iran-International Agency for Research on Cancer Study Group, 1977).
In a subsequent case-control study in this region, investigators also
found that cases had consumed smaller amounts of uncooked vegetables
(as well as fruits) than had controls (Cook-Mozaf fari, 1979; Cook-
Mozaffari et_ al. , 1979) .
Stomach. Among other findings, Hirayama (1967) reported an
inverse association between daily consumption of milk (a vitamin A
source) and stomach cancer in a case-control study in Japan. More
recently, Hirayama (1977) reported a similar "protective" effect of
milk based on data from a prospective cohort study involving 265,118
subjects. There was also a lower risk for stomach cancer among non-
smokers who consumed green and yellow vegetables.
Graham et al. (1972) reported higher consumption of uncooked
vegetables "nTiEely sources of 3 -carotene) by controls than by cases
in a case-control study of gastric cancer in New York State. A simi-
lar inverse association with consumption of raw vegetables was noted
by Haenszel e al. (1972) in a case-control study in Hawaii.
Colon/ Rectum. In ongoing cohort studies in Norway and Minnesota,
Bjelke (1978) has found that milk and several vegetables have been
consumed with less frequency by colorectal cancer cases than by
controls. An index of vitamin A intake (which was highly correlated
with consumption of vegetables) showed the same inverse relationship.
Prostate. In a study on prostate cancer, Schuman et^ al_. (1982)
found that foods rich in vitamin A (e.g., liver) and g -carotene (e.g.,
carrots) were consumed less frequently by cases than by controls.
General . In three recent reports based on data from cohort studies
in the United States and England, the investigators observed that there
was an inverse relationship between serum levels of vitamin A and sub-
sequent risk of cancer in general (Cambien et^ al. , 1980; Kark et al.,
1980; Waldjet al. , 1980). The relationship between dietary intake of
vitamin A and its level in serum (which is under homeostatic control)
is not yet clear in populations si^ch as these, which are generally not
deficient in this nutrient.
9-4
Experimental Evidence
In the following discussion, the term "vitamin A" is used to
include: vitamin A itself, synthetic analogues of vitamin A called
retinoids, and naturally occurring plant constituents, the carote-
noids, which can be converted to vitamin A in vivo*
Vitamin A is necessary for normal differentiation of epithelial
cells in many tissues. A deficiency of this vitamin results in
metaplasia, a pathological condition in which a keratinizing squamous
epithelium replaces the form of epithelium that is normal to various
tissues (Wolbach and Howe, 1925). In the bronchial mucosa, for ex-
ample, the mucus-secreting columnar epithelium is replaced by a
stratified squamous epithelium. Of relevance to the relationship
between vitamin A and cancer is the occurrence of metaplasia, early
in the evolution of many neoplasms. In the tissue undergoing malig-
nant transformation, the normal differentiation pattern is lost and
a new form of epithelium appears.
Vitamin A Deficiency. Since the appearance of metaplasia is
common to both vitamin A deficiency and early neoplasia, a defi-
ciency of this vitamin might enhance the neoplastic response to
chemical carcinogens. In vitro experiments in organ cultures have
supported this concept. In an organ culture of mouse prostatic
tissue, vitamin A was shown to prevent the induction of metaplasia
induced either by a culture medium deficient in vitamin A or by
carcinogenic polycyclic aromatic hydrocarbons (Lasnitzki, 1963). In
organ cultures of hamster tracheas, vitamin A inhibited the induction
of squamous cell metaplasia and proliferative epithelial lesions by
benzo[ajpyrene (Crocker and Sanders, 1970).
Some in vivo experiments have produced similar results. For ex-
ample, Nettesheim and Williams (1976) reported that the induction of
neoplastic lesions of the lungs by 3-methylcholanthrene was enhanced
in rats deprived of vitamin A intake. This conclusion was based on
observations of squamous nodules In the lungs, which have been demon-
strated to be precursors of squamous cell carcinomas. Vitamin A de-
ficiency also affects the mucosa of the urinary bladder, producing
squamous cell metaplasia as well as a high incidence of cystitis,
ureter! tis, and pyelonephritis. The effects of vitamin A defi-
ciency have been investigated in rats given N-[4-(5-ni tro-2-furyl) -
2-thiazolyl]-formamide (FANFT), a compound that causes cancer of the
bladder. In Sprague-Dawley rats maintained on a diet deficient in
vitamin A, there was an acceleration in the neoplastic response to
FANFT, resulting in an earlier appearance of urinary bladder tumors
and the development of ureteral and pelvic carcinomas (Cohen et al.,
1976). :
Although squamous cell metaplasia in the mucosa of the large bowel
does not occur with vitamin A deficiency, several studies have been
9-5
conducted to determine the effect of such a deficiency on carcinogen-
induced neoplasia of the large bowel in the rat (Narlsawa et_ al_ . , 1976;
Newberne and Rogers, 1973; Rogers e al . , 1973). Rogers et aJU (1973)
studied the effects of a low vitamin A intake on response of rats to
intragastric administration of 1,2-dimethylhydrazine. They obsefved a
slight increase in the incidence of tumors of the large bowel in the
animals on the low vitamin A diet. Different results were obtained by
Narisawa et_ al. (1976), who administered the carcinogen N-me thy 1-N 1 -
nitro-N-nitrosoguanidine (MNNG) intrarectally to rats. In this study,
animals fed a diet free of vitamin A developed fewer neoplastic lesions
of the large bowel than those supplemented with vitamin A or fed a
commercial chow diet with adequate vitamin A content.
An experiment of a somewhat different nature was conducted by
Newberne and Rogers (1973). In this study, rats were exposed to the
carcinogen aflatoxin and were fed diets containing various amounts of
vitamin A. Animals deficient in vitamin A developed tumors of the
large bowel, whereas rats fed a diet containing adequate amounts of
vitamin A did not. Neoplasms of the liver developed in both groups of
animals; however, there were fewer liver tumors in the group deficient
in vitamin A. Thus, the overall effect was a shift in site of neo-
plasms rather than an overall change in tumor incidence (Newberne and
Rogers, 1973).
In summary, studies in animals indicate that a deficiency of
vitamin A can result in an increased susceptibility to carcinogen-
induced neoplasia; however, there are exceptions.
Excess Intake of Vitamin A. Investigations have also been con-
ducted to determine the effect of excess vitamin A on the occurrence of
neoplasia in animals. Saffiotti e aJ . (1967) demonstrated that a high
intake of vitamin A protected against benzo[ajpyrene-induced metaplasia
and squamous cell neoplasms of the tracheobronclal tree In hamsters.
Supporting data reported by Nettesheim and Williams (1976) Indicated
that vitamin A protects against 3-methylcholanthreiLe-Induced squamous
cell metaplasia and early neoplastic lesions of the lung in rats. In
contrast, Smith t_ alL. (1975) observed that an intake of high levels of
vitamin A increases the incidence of respiratory tract tumors in ham-
sters. Retinyl acetate has also been shown to enhance hormone-induced
mammary tumorigenesis in female GR/A mice (Welsch et al. f 1981). In
studies of other target sites, Chu and Malmgren (1965T~and Shamberger
(1971) observed that a high intake of vitamin A inhibited formation of
tumors of the forestomach and cjfvix in hamsters and the skin of mice*
Rogers e^ cjJU (1973) reported that the induction of neoplasia In the
large bowel of ra^ts by 1,2-dimethylhydrazine (DMH) was slightly
enhanced by a high intake of the vitamin.
To summarize, studies in animals indicate that an increased intake
of this vitamin has a protective effect against the induction of cancer
by chemical carcinogens in most, but not all, instances.
9-6
Retinoids. Results from the studies of vitamin A have stimulated
efforts to find analogues with a greater inhibitory effect on neoplasia,
less toxicity, and a capability of reaching target tissues in concentra-
tions higher than those of the naturally occurring vitamin. Many such
compounds, the retinoids, have been synthesized, but are not normal con-
stituents of the diet. Experiments to study the inhibition of carcino-
gen-induced neoplasia of the breast, urinary bladder, skin, and lung by
these analogues have produced impressive results (see review by Sporn
and Newton, 1979, 1981; Sporn et_ a^. , 1976). These compounds have also
been responsible for regression of skin papillomas in mice (Bollag,
1971). The effects of these compounds buttress observations from
studies of naturally occurring vitamin A.
Carotenoids. In plants there is a group of compounds, the carote-
noids, that can be converted into vitamin A _in vivo. These compounds
can also be absorbed unchanged from the gastrointestinal tract and
exist in tissues in their original form. In a recent review of epi-
demiological data on vitamin A and related compounds, Peto et al.
(1981) considered the possibility that 3 -carotene itself rather than
its derivative, vitamin A, may have the capacity to inhibit carcino-
genesis in epithelial cells. Only a few studies have been conducted
to investigate the effects of carotenoids on neoplasia in laboratory
animals. Recently, Mathews-Roth et_ al. (1977) observed that $-caro-
tene, canthaxanthin (4-4 f -dike t o- g -carotene) , and phytoene can produce
a significant protective effect against the development of UV-induced
skin tumors in hairless mice. Since canthaxanthin and phytoene are
carotenoids that do not have vitamin A activity, the protective effect
appears to reside in the carotenoid structure per se. In an earlier
study, Shamberger (1971) reported experiments in which 3-carotene
applied to the skin of mice concomitantly with croton oil increased the
formation of epidermal tumors previously initiated by 7,12-dimethylbenz-
[aj anthracene (DMBA) . Considerable further research is necessary to
evaluate the effects of carotenoids on carcinogenesis in laboratory
animals.
Summary
Epidemiological Evidence. A growing accumulation of epidemiologi-
cal evidence indicates that there is an inverse relationship between
the risk of cancer and the consumption of foods containing vitamin A
(e.g., liver) or its precursors (e.g., some carotenoids in dark green
and deep yellow vegetables) . Most of the data, however, do not show
whether the effects are due to carotenoids, to vitamin A itself, or to
some other constituents of these foods. In these studies, investigators
found an inverse association between estimates of "vitamin A" intake
and carcinoma at several sites, e.g., the lung, the urinary bladder,
and the larynx. All these cancers involve epithelial cells.
Experimental Evidence. Studies in animals indicate that vitamin A
deficiency generally increases susceptibility to chemically induced
9-7
neoplasia, and that an increased intake of the vitamin appears to pro-
tect against carcinogenesis in most, but not all, cases. Because high
doses of vitamin A are toxic, many of these studies have been conducted
with its synthetic analogues, retinoids, which lack some of the toxic
effects of the vitamin. These analogues have been shown to inhibit
chemically induced neoplasia of the breast, urinary bladder, skin, and
lung.
Conclusion
The committee concluded that the laboratory evidence shows that
vitamin A itself and many of the retinoids are able to suppress chemi-
cally induced tumors. The epidemiological evidence is sufficient to
suggest that foods rich in carotenes or vitamin A are associated with a
reduced risk of cancer. The toxicity of vitamin A in doses exceeding
those required for optimum nutrition, and the difficulty of epidemio-
logical studies to distinguish the effects of carotenes from those of
vitamin A, argue against increasing vitamin A intake by the use of
supplements.
VITAMIN C (ASCORBIC ACID)
Epidemiological Evidence
The associations of vitamin C with cancer in epidemiological stud-
ies are mostly indirect since they are based on the consumption of
foods known to contain high concentrations of the vitamin. In general,
the data suggest that vitamin C may lower the risk of cancer, particu-
larly in the esophagus and stomach.
In 1964, Meinsma noted that the consumption of citrus fruits by
cases of gastric cancer was lower than that by controls. Similar
inverse associations between fresh fruit consumption or vitamin C
intake and gastric cancer have been reported by Higginson (1966),
Haenszel and Correa (1975), Bjelke (1978), and Kolonel et al . (1981).
These observations are consistent with the hypothesis that vitamin C
protects against gastric cancer by blocking the reaction of secondary
and higher amines with nitrite to form nitrosamines (Correa et al.,
1975).
As noted in the discussion of vitamin A, Mettlin et_ al. (1981)
found inverse associations of indices of both vitamin A and vitamin
C consumption with esophageal cancer, based on frequency of consump-
tion of selected food items by male cases and controls. The rela-
tionship was stronger for vitamin C than for vitamin A, however 4 and
only the association with vitamin C was statistically significant
after controlling for smoking and alcohol use. In studies of humafi
populations on the Caspian littoral of Iran, inverse associatibns hav<e
9-8
been found between esophageal cancer and consumption of fresh fruits
and estimated intake of vitamin C, based on correlational and case-
control data (Cook-Mozaffari, 1979; Cook-Mozaf fari et^ al. , 1979;
Hormozdiari et^ ad . , 1975; Joint Iran-International Agency for Research
on Cancer Study Group, 1977).
A protective role for vitamin C in laryngeal cancer was also
inferred in a case-control study conducted by Graham et_ al . (1981).
These investigators found an inverse relationship between cancer risk
and indices of both vitamins C and A, after controlling for cigarette
smoking and alcohol consumption. There was a similar relationship for
vegetable consumption in general, but not for cruciferous vegetables in
particular.
Wassertheil-Smoller e al* (1981) recently reported a similar
inverse association between vitamin C consumption (calculated from
analysis of 3-day records of foods and a 24-hour recall) and uterine
cervical dysplasia in a case-control study of women in New York. The
findings persisted after the investigators controlled for age and
sexual activity in the analysis.
In contrast, Jain et al. (1980) found no association between
vitamin C consumption and colon cancer in a case-control study based
on quantitative data obtained from dietary histories.
Experimental Evidence
Vitamin C has also been studied for its effects on cancer under a
variety of experimental conditions. The simplest studies are those
that have demonstrated that ascorbic acid can prevent the reaction of
nitrites with amines or amides to form carcinogenic nitroso compounds.
Ascorbic acid effectively competes for the nitrite, thereby inhibiting
the formation of the carcinogenic nitroso compounds (Ivankovic et al. ,
1975; Mirvish, 1981; Mirvish e ad. , 1972, 1975). Investigations of
this phenomenon in vitro and in vivo have been published by a number
of scientists. In a prototype in vitro study, Mirvish et_ aJU (1972)
demonstrated that ascorbic acid inhibited formation of nitroso com-
pounds resulting from the reaction of nitrites with oxytetracycline,
morpholine, piperazine, NHmethylaniline, methylurea, and dime thy lamine-
In subsequent in vivo studies, they showed that ascorbic acid inhibits
formation of nitroso carcinogens in mice (Mirvish et al. , 1975). In
their experimental model, Swiss and Strain A mice were fed amines or
amides in the diet and were given nitrite in, their drinking water.
Under these conditions, pulmonary tumors developed. The addition of
ascorbic acid to the diet resulted in a marked inhibition of these
tumors. Ascorbic acid also consistently produced an inhibitory effect
in other in vivo studies when nitrite and $$&fto compounds were admin-
istered by the same routes (Ivankovic et *il^ 1975; Mirvish* 1981;
Rustia, 1975).
The effect of vitamin C on carcinogenesis resulting from exposures
to already formed carcinogens is not clearly understood. Experiments
9-9
the only laboratory animal that, like primates, does not synthesize
vitamin C. Moreover, the endogenous synthesis of vitamin C responds
easily to various stimuli, e.g., exposures to certain xenobiotic
compounds. Data presented in two abstracts indicate that ascorbic acid
inhibited neoplasia of the large bowel in rats given 1, 2-^dimethylhydra-
zine (Logue and Frommer, 1980; Reddy and Hirota, 1979). Kallistratos
and Fasske (1980) reported that administration of a high dose of
ascorbic acid in the diet of rats inhibited the induction of sarcoma by
benzo[ajpyrene. Only a few animals were used in this investigation.
Soloway et al. (1975) reported that ascorbic acid had no effect on the
occurrence of neoplasia in the rat bladder after administration of
FANFT. Overall, the reported protective effects of ascorbic acid on
neoplasia are not impressive, except for those brought about through an
indirect mechanism, i.e., the prevention of the formation of carcino-
genic N-nitroso compounds. In only two instances have investigators
reported inhibition of carcinogenesis in the same tissue, i.e., the
large bowel (Logue and Frommer, 1980; Reddy and Hirota, 1979).
However, since these studies were reported only in abstract form, their
results warrant further investigation.
In a study with a small number of guinea pigs, a high dietary
intake of ascorbic acid had a slight enhancing effect on the induction
of sarcoma by 3-methylcholanthrene (Banic, 1981). Russell et al.
(1952) also studied the induction of sarcoma by the same compound in
three groups of guinea pigs: a group deficient in vitamin C, a group
receiving vitamin C but on a food-restricted diet, and a group fed ad
libitum. The number of animals developing tumors was similar in all
three groups, but the latent period was slightly shorter in the vita-
min-C-deficient group, indicating that the response produced by vitamin
C deficiency was very slight or nonexistent.
Recently, observations on the effects of vitamin C on cells in
culture have indicated that ascorbic acid can affect cellular mani-
festations of malignancy. When C3H/10T1/2 mouse embryo cells are
exposed to 3-methylcholanthrene, morphological transformation occurs.
However, the transformation is prevented if ascorbic acid is added to
the culture medium. Addition of the ascorbic acid as late as 23 days
after the treatment with 3-methylcholanthrene still completely inhibits
transformation. Under some circumstances, it is possible to cause
reversion of chemically transformed cells to normal-appearing morpho*-
logical phenotypes by adding ascorbic acid to the culture medium
(Benedict et_ al , 1980). The mechanism for inhibition and reversion
is presently unknown.
The effects of ascorbic acid on human leukemia cells in culture
have also been studied. Low concentrations of ascorbic a&id were
found to suppress growth of human leukemia cells from patients with
acute nonlynipfaoeytic leukeuila under conditions in which growth of
normal myeloid colonies was not suppressed (Park et al., 1980).
9-10
Summary
Epidemiological Evidence . The epidemiological data pertaining to
the effect of vitamin C on the occurrence of cancer are not extensive.
Furthermore, they provide mostly indirect evidence since they are based
on the consumption of foods, especially fresh fruits and vegetables,
known to contain high concentrations of the vitamin, rather than on
actual measurements of vitamin C intake. The results of several case-
control studies and a few correlation studies suggest that the consump-
tion of vitamin-C-containing foods is associated with a lower risk for
certain cancers, particularly gastric and esophageal cancer.
Experimental Evidence. In the laboratory, ascorbic acid can in-
hibit the formation of carcinogenic N-nitroso compounds, both in vitro
and in vivo. On the other hand, studies of its inhibitory effect on
the action of preformed carcinogens have not provided conclusive
results. In recent studies, the addition of ascorbic acid to cells
grown in culture prevented the chemically induced transformation of
these cells and, in some cases, caused reversion of transformed cells.
Conclusion
The limited evidence suggests that vitamin C can inhibit the
formation of some carcinogens and that the consumption of vitamin-C-
containing foods is associated with a lower risk of cancers of the
stomach and esophagus.
VITAMIN E (a-Tocopherol)
Epidemiological Evidence
There are as yet no epidemiological data associating vitamin E with
cancer risk, and such data may prove difficult to obtain for several
reasons. First, vitamin E is present in a wide variety of foods (e.g.,
vegetable oils, whole grain cereal products, and eggs), which makes it
difficult to identify groups of people with substantially different
levels of intake. In addition, a clear-cut deficiency has not been
established in humans. Vitamin E is also relatively unstable during
storage, and its concentration can vary greatly within individual
foodstuffs.
Experimental Evidence
Of the various tocopherols, vitamin E (ot-tocopherol) is most
widely distributed among different foods and has the greatest biologi-
cal activity (Harris * al^ , 1972). The vast majority of studies of
the relationship of the tocopherols and cancer have been conducted
9-11
with a-tocopherol. Like vitamin C, a-tocopherol competes for availa-
ble nitrite, thereby blocking the formation of carcinogenic nitroso
compounds from reactions between nitrite and nitrosatable substrates
such as amines or amides (Fiddler et al * , 1978; Mergens t aJL . , 1978,
1979). An important difference between these vitamins is their solu-
bility. Ascorbic acid is water soluble, whereas a-tocopherol is sol-
uble in lipids. Thus, the inhibitory effects of ot-tocopherol would
take place largely in a lipid milieu.
There have been no in vivo studies to determine the effects on
neoplasia resulting from a~tocopherol-induced inhibition of nitroso
compound formation. However, Kamm e_t_ aJU (1977) have reported that the
in vivo formation of nitrosamines from precursor compounds resulted in
hepatotoxicity. In this study, rats were intubated with a solution
containing sodium nitrite and aminopyrene. This was followed by oral
administration of a-tocopherol or vehicle. Animals receiving the
vehicle had elevated SGPT (serum glutamic-pyruvic transaminase) , indi-
cating liver damage. Rats receiving a-tocopherol had either a lower
elevation of SGPT or no elevation at all, depending on the dose of
ot-tocopherol administered. These investigators also reported that the
rats receiving a-tocopherol had a markedly lower level of nitrosamines
in their serum than did the corresponding controls.
Efforts to inhibit neoplasia by administering increased amounts of
vitamin E have a long history. In one of the earliest studies, Jaffe
(1946) reported that the number of mixed tumors resulting from intra-
peritoneal injection of 3-methylcholanthrene was lower in rats re-
ceiving a diet with added wheat germ oil than in rats on a control
diet. Subsequently, Haber and Wissler (1962) studied the effect of
ot-tocopherol supplements on subcutaneous sarcomas induced by injecting
mice with 3-methylcholanthrene. Their data suggested that a -tocopherol
inhibited the occurrence of these sarcomas. In studies by Epstein et
al. (1967), a-tocopherol and a number of other phenolic antloxidants
did not suppress the formation of subcutaneous sarcomas induced in mice
by injections of 3,4 ,9,10-dibenzpyrene. More recently, Wattenberg
(1972) reported that addition of a-tocopherol to the diet prior to
administration of the carcinogen failed to inhibit DMBA-induced
neoplasia of the forestomach of mice.
i
Several investigators have studied the effects of a-tocopherol on
DMBA-induced formation of mammary tumors. Wattenberg (1972) reported
that ingest ion of high levels of a-tocopherol only during the period
before DMBA was administered did not inhibit the occurrence of mammary
tumors. In a brief report, Harman (1969) presented data showing that a
large vitamin E supplement im a semipurified diet fed from 11 days
prior to DMBA administration until completion pf the study decreased
the number of tumor-bearing rats by slightly less tlian ome^half In
another brief report, Leet and Chen (1979) indicated tihat ipats fed die|$
either lacking a-tocopherol op containing ope-half the minimum level
recommended had an increased! tumor incidence as compared to animals
receiving a diet with adequate or excessive amounts of vitamin E.
9-12
The effects of vitamin E on epidermal neoplasia have also been
studied. In one study, an increased intake of vitamin E was reported
to have no inhibitory effect in mice (Wattenberg, 1972); in another, it
was observed to produce a small degree of inhibition of mammary tumors
in rats (Lee and Chen, 1979). Shamberger (1970) reported that addition
of vitamin E to a solution containing tumor promoters (e.g., croton
oil, croton resin, and phenol) inhibited formation of tumors in some
instances, but this was not a consistent effect.
Cook and McNamara (1980) compared the effects of high and low
doses of vitamin E on dimethylhydrazine-induced neoplasia in the large
intestine of mice. The diet fed to the mice consisted of natural^
constituents fortified by vitamins and minerals, and contained 26%
fat. Although the tumor incidence was similar in both groups, the
average number of tumors per animal was less in the high vitamin E
group than in the low vitamin E group.
Studies of the effects of vitamin E on carcinogenesis do not show
severe or consistent inhibitory effects* It is possible that vitamin E
can inhibit under certain conditions, but a reproducible experimental
model in which vitamin E consistently inhibits neoplasia has not yet
been found .
Summary and Conclusions
There are no reports of epidemiological studies concerning vitamin
E intake and the risk of cancer.
Vitamin E (a-tocopherol) , like ascorbic acid, inhibits the formation
of nitrosamines in vivo and in vitro. However, there are no reports on
the effect of this vitamin on nitrosoamine-induced neoplasia. There is
limited evidence suggesting that vitamin E may inhibit tumorigenesis in
several model systems.
The data are not sufficient to permit any firm conclusion to be
drawn about the effect of vitamin E on cancer in humans.
CHQLINE AND SELECTED B VITAMINS
Since the B vitamins are essential components of any adequate diet
and are necessary for the continued maintenance of cellular integrity
and metabolic function, severe deficiencies in any of them will clearly
reduce the growth rate of tumor cells and interfere with the normal
functioning of the organism (Young and Newberne, 1981). However, only
a few of these vitamins, such as thiamine, riboflavin, pyridoxine, vita-
min B^2> and folic acid, are discussed in this chapter because data
for others are inadequate. Choline, although not a vitamin by strict
definition, is generally included in the vitamin B complex. To consider
9-13
the roles of choline and the B vitamins in carcinogenesis, one must
recognize the complex interrelationships of these vitamins with each
other and with other components of diet, such as dietary protein and
total calories. For example, secondary changes in protein, nucleic
acid, carbohydrate, fat, and/or mineral metabolism can account for
many of the effects observed with specific vitamins. Thus, although
certain models have defined the roles of several of these vitamins at
the molecular level, their overall contribution to modulation of car-
cinogenesis is difficult to assess.
Epidemiological Studies
No epidemiological studies have been conducted on the role of the B
vitamins in carcinogenesis.
Experimental Studies
In much of the work demonstrating effects of specific B vitamins
on carcinogenesis in model systems, there has been no control for
intake of other dietary constituents, notably protein and calories.
Thus, many results of such efforts are not useful since these two
major components have considerable effect on the overall outcome of
carcinogenesis. Notable early exceptions are studies by Tannenbaum
and by Boutwell. These studies show that intake of B vitamins has
either no effect, or at most a minimal effect, on carcinogenesis.
Tannenbaum and Silverstone (1952) reported that there were no signifi-
cant differences in the incidence of tumors among groups of animals fed
minimal, moderate, or high levels of the B vitamins. In three of four
experiments, however, the rate of tumor development was faster in mice
ingesting moderate amounts of vitamins than in mice ingesting either
high or low amounts. Boutwell e ajL. (1949) detected no effects of
specific components, although when intake of alj, B vitamins was low,
the incidence of tumors in mice was decreased.
Enzymatic activation or deactivation of procarcinogens involves
competing pathways. These metabolic pathways can be modulated by di-
etary constituents such as vitamins and other nutrients, which in turn
modulate carcinogenesis. For example, Kensler e l. (1941) demon-
strated that riboflavin provided partial protection against hepatic
cancer caused by orally administered dimethylaminoazobenzene in rats by
enhancing the detoxification of that carcinogen by a flavin-dependetit
enzyme system (Miller and Miller, 1953; Miller e al . , 1952). It seems
likely that the opposite effect, i.e., enhancement of carcinogenic
potential, might be observed if vitamin 82 (riboflavin) Were required
for activation to the ultimate carcinogen. The cumulative effect of
riboflavin-supplemented diets on tiepatocarcinogenesis caused by other
compounds and on tumorigenesis at other sites has not been adequately
assessed. Thus, despite the existence of one clearly defined effect,
which has a molecular basis, it is difficult to generalize about the*
role of vitamin 83 in carcinogenesis.
9-14
The complex interrelationships between the B vitamins and other
dietary components have been thoroughly examined in studies of diets
deficient in lipotropes (e.g., methionine, choline, and folate) and
high in fat content (Rogers and Newberne, 1980). Although the major
lipotropes are choline and methionine, folate (and to some extent
vitamin B^) can also exert lipotropic action. Modulation of
carcinogenesis by other vitamins, such as inositol and vitamin Bg,
may contribute to the overall lipotropic activity of these diets.
Individual B vitamins may have enhancing effects on carcinogenesis,
depending on experimental conditions. Thus, only carefully controlled
experiments can shed light on the specific contribution of each of the
B vitamins. The overall results clearly demonstrate that the effects
of B vitamins on carcinogenesis depend on the specific chemical car-
cinogen, the target organ, and the strain and sex of the animal. The
relative importance of the individual dietary components may vary,
depending on experimental conditions.
The relationship of the results of the short-term tests to those
from in vivo studies for carcinogenicity of chemicals in animals adds
a further complication. These differences in the findings from these
two types of studies have been reviewed for various compounds includ-
ing aflatoxin B^ (Rogers and Newberne, 1969), N-nitrosodiethylamine
(Rogers, 1977), N-nitrosodibutylamine, N-nitrosodimethylamine, N-2-
f luorenylacetamide , 7 , 12-dime thylbenzanthracene , 1 , 2-dime thylhydra-
zine, and 3,3~diphenyl-3-dimethylcarbamyl-l-propine (Rogers and
Newberne, 1980). Rogers and Newberne (1980) observed that the most
consistent results obtained with lipotrope-def icient diets in rats were
enhancement of hepatocarcinogenesis and, to a lesser extent, of colon
carcinogenesis. These diets do not have a consistent effect on tumor
induction in target organs other than the liver and colon (Rogers,
1977). In many cases, abnormalities in the metabolism of carcinogens
can be demonstrated; however, their effects on tumor incidence cannot
always be predicted.
Recently, considerable effort has been expended to determine
whether or not the metabolism and transport of vitamins or the binding
of the appropriate coenzyme forms to apoenzymes are altered in tumor
cells (Thanassi e al. , 1981; Tryfiates, 1981). For instance, in
Morris hepatoma cells, the transport and phosphorylation of pyridoxine
appear to be severely impaired (Thanassi e al . , 1981). Effects on
the metabolism of riboflavin have also been reported t^ivlin, 1973),
but it is not known whether the observed alterations have any influence
on the modulation of carcinogenesis. The alterations in vitamin B
metabolism may be due to secondary changes in the metabolism of amino
acids, especially tryptophan (Bell, 1980; Sell et al., 1972; By#r and
Blackard, 1977). , ~~ ~ :
The effects on carcinogenesis by the B vitamins cannot be ascribed
solely to effects modulating the stages of initiation or promotion
9-15
(Pitot and Sirica, 1980). These vitamins may also modulate other
processes such as immunosurveillance, which may affect the ultimate
outcome of carcinogenesis. Impairment of the immune function has been
demonstrated in pyridoxine-deficient animals (Axelrod and Trakatellis,
1964), and it seems likely that major disruption of energy or carbohy-
drate metabolism by deficiencies of riboflavin or thiamine, as well as
disruption of normal cell replication by deficiencies in folate or
vitamin B^2, would affect immune surveillance* Because of the inter-
relationships among the B vitamins and their relationships with other
major dietary components, it is difficult to explain specifically the
effects on promotional events (Diamond t^ l/ > 1980).
The modulation of carcinogenesis by the B vitamins under conditions
of normal dietary intake is probably minimal. However, a change of in-
take of a specific B vitamin may be warranted when a specific chemical
carcinogen is present.
Summary and Conclusions
The relationship of dietary B vitamins to the occurrence of cancer
has not been studied epidemiologically. There have been a few inade-
quate laboratory investigations to determine whether there is a rela-
tionship between the various B vitamins and the occurrence of cancer.
Therefore, no conclusions can be drawn.
9-16
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CHAPTER 10
MINERALS
Very few epidemiological studies have been conducted to determine
the relationship between minerals and the incidence of cancer in humans.
This is due partly to the difficulty of identifying populations with
significantly different intakes of the various minerals. In contrast,
there have been numerous studies in laboratory animals. In these in-
vestigations, the carcinogenic effects of many metals, administered at
high doses to the animals parenterally, have been well established and
have been reviewed extensively (Furst, 1979; Sunderman, 1977). However,
the results of these studies have shed little light on the potential
carcinogenic risk posed by trace elements in the amounts occurring
naturally in the diet of humans.
Very few feeding studies have been conducted to test the carcino-
genicity of trace elements in animals. The carcinogenic action of these
elements is difficult to test in animals because some of them are toxic
at levels that exceed dietary requirements, and because it is diffi-
cult to control synergistic interactions of the element under investiga-
tion with other elements that may contaminate air, diet, and drinking
water. This chapter contains an evaluation of a few of those trace
elements that are nutritionally significant and suspected of playing a
role In carcinogenesis. The committee sought evidence primarily from
those experiments in which the element was fed to the animal or from
epldemiological reports of exposure through diet. Results obtained from
laboratory experiments using other routes of exposure, or evidence from
occupational exposure of humans, are described briefly when sufficient
information about dietary exposure could not be found. The effects of
both the deficiencies as well as excessive intakes of minerals are also
discussed in this chapter*
Schroeder and his associates investigated the carcinogenicity of
trace elements in a series of large experiments extending over 15 years
(Kanisawa and Schroeder, 1967; Schroeder and Kitchener, 1971a,b, 1972;
Schroeder e al. , 1964, 1965, 1968, 1970). Animals were raised in an
environment that permitted maximum control of trace element contamina-
tion; they were fed one diet of known composition; and they were observed
for their lifetime. The following elements were studied in at least 50
mice and/or rats per treatment: fluorine, titanium, vanadium, chromium,
nickel, gallium, germanium, arsenic, selenium, yttrium, zirconium, nio-
bium, rhodium, palladiiiii, cadmium, Indium, tin, antimony, tellurium, and
lead. These elements were added to the drinking water at levels of 5
mg/liter, except foe selenium (3 mg/liter) and tellurium (2 mg/liteir).
These levels (approximately 100 times greater than the concentrations
present naturally in the diet) did not significantly affect growth and
survival of the animals. The interpretation of these findings of no
10-2
effects or minimally significant effects must be cautious, in view of the
small number of animals used. Only rhodium and palladium (tested in mice
only) showed any signs of carcinogenicity, but as Schroeder and Michener
(1971a) stated, "The results were at a minimally significant level of
confidence." Further studies are needed to confirm these findings.
Schroeder also reported that selenate, but not selenite, increased the
incidence of spontaneous malignant mammary and subcutaneous tumors in
rats after lifetime exposure (11 in 75 controls vs 20 in 73 selenate-fed
animals). These results were not confirmed in similar studies in mice.
(The effects of selenium on carcinogenesis are discussed in further
detail below.) None of the remaining elements examined increased tumor
incidence. A significant reduction in tumor incidence was observed in
mice fed arsenic and cadmium and in mice and rats fed lead.
SELENIUM
Signs of chronic selenium toxicity in animals have been recognized
for almost 700 years, but selenium was not identified as the responsible
agent until the 1930 f s. Twenty years later, the economic importance of
selenosis and selenium deficiency for animal producers became apparent.
This discovery stimulated the mapping of selenium distribution in the
soils, forages, and tissues of humans in several continents. Extreme
differences of exposure were delineated, even within individual countries*
This knowledge enabled investigators to make epidemiological correlations
of diseases, including cancer, in humans and animals and to conduct lab-
oratory experiments to test the resulting hypotheses (National Academy of
Sciences, 1971).
Epidemiological Evidence
Selenium has been reported as having a possible protective effect
against cancer. Shamberger and colleagues correlated selenium levels
in forage crops (grouped into high, medium, and low categories) with
cancer mortality by state in the United States (Shamberger and Frost,
1969; Shamberger and Willis, 1971; Shamberger et, al. , 1976). They
found an inverse relationship in both males and females, especially
for cancers of the gastrointestinal and genitourinary tracts. In other
studies, Schrauzer and coworkers correlated per capita intake with cancer
mortality rates in more than 20 countries (Schrauzer, 1976; Schrauzer et
al. , 1977a,b). The consumption estimates were based on international
food disappearance data for major food sources (e.g., cereals, meat, and
seafoods) to which the investigators attributed plausible mean selenium
values. They found an inverse relationship between selenium intake and
leukemia as well as with cancers of the colon, rectum, pancreas, breast,
ovary, prostate, bladder, lung (males), and skin. Using pooled blood
samples from healthy donors in 19 U.S. states and 22 countries, they also
correlated blood levels of selenium with corresponding cancer mortality
rates. They found significant inverse relationships for most of these
same sites.
10-3
Shamberger et al. (1973) compared the blood selenium levels in
more than 100 cancer patients with those in 48 normal subjects attend-
ing a clinic. The levels in patients with gastrointestinal cancers
and Hodgkin's disease were significantly lower than those in the normal
subjects, but there were no differences between the normal subjects and
patients with cancers at other sites, such as the breast. It is not
clear from this study whether the observed difference in the selenium
levels was the result or the cause of the cancers.
Jansson et_ aJ . (1975, 1978) examined cancer mortality rates in the
United States by county. They compared the rates in the northeastern
part of the country with corresponding levels of selenium in the water
supply. In contrast to other investigators, they reported a direct
correlation between mortality from colorectal cancer and selenium levels
in the drinking water.
Experimental Evidence
Carcinogenicity. During the past 40 years selenium has been alter-
nately described as a carcinogen and an anticarcinogen, on the basis of
experiments on animals. Because studies conducted during the 1940 f s
showed that high levels of selenium induced or enhanced tumor formation,
the Food and Drug Administration until recently prohibited the enrichment
of animal feeds with selenium, even in areas with established selenium
deficiency. In contrast to the results of the earlier investigations,
more recent studies by several independent investigators have established
that dietary selenium has a protective effect against tumors induced by a
variety of chemical carcinogens or at least one viral agent.
A critical review of the experimental conditions suggests that the
earlier studies demonstrating carcinogenic or promoting properties of
selenium can be faulted on the basis of experimental design* Nelson et
ad. (1943) fed a 12% protein diet to 18 control rats and to 126 rats
whose diet was enriched with selenium (5, 7, and 10 jag/g) as seleniferous
grain or selenldes. Fifty-three of the test animals and 14 of the con-
trols survived to an age of 1.5 to 2 years. The livers of the control
rats were normal, but all animals fed the 'high selenium diet had liver
cirrhosis. Of these, 11 had developed nonmetastasizing adenomas and the
rest showed hyperplasia. These findings can be attributed to a combina-
tion of two insults: the near toxic levels of selenium and the marginal
protein content of the diet.
Harr et al. (1967) investigated the effect of selenium on tumor
formation in 1,437 rats fed a range of selenium levels for as long as 30
months. Eighty-eight rats were also fed 2-acetylaminof luorene (2-AAF)
along with selenium. The experimental design also included a repetition
of the earlier experiment by Nelson et'ial^ (1943), i.e., a marginal pro-
tein diet was supplemented with selenium as selenate at 0.5, 2.4, or 8
u8/g- As expected, diets containing selenium in concentrations
10-4
higher than 8 ug/g were toxic and killed the rats within the first
month. The rats fed the two lower levels survived for more than a year.
Autopsies and histological examinations performed on 1,123 of the rats on
various dietary treatments provided no evidence for a carcinogenic effect
of selenium. Forty-three tumors occurred in 88 of the rats fed 50 or
100 yg/g of AAF diet without added selenium; the rest of the autopsied
animals exibited 20 neoplasms, randomly distributed, regardless of the
level of dietary selenium. Although there were no hepatic tumors in any
autopsied animals that did not receive the carcinogen, approximately half
of the selenium-supplemented rats that survived for more than 9 months
had hyperplastic lesions in the liver, whereas none occurred in the
controls.
In another series of studies, Volgarev and Tscherkes (1967) measured
the effect of selenium in 200 rats, but they did not use a selenium-
free control group. In the first experiment, 40 rats were fed selenium
as selenate at 4.3 to 8.6 Pg/g of diet. All animals developed liver cirr-
hosis, 10 had neoplastic tumors, 4 had precancerous lesions, and 9 were
unaffected. In a second experiment, only 5 neoplasms were observed among
60 rats. The third experiment failed to produce any tumors in 100
animals.
Schroeder and Kitchener (1971b, 1972) studied the effect of se-
lenium supplementation (2 to 3 mg/liter in drinking water as selenate
or selenite) in lifetime experiments with rats and mice. Neither form
of selenium affected the incidence of tumors in mice, and selenite had
no effect in rats. Specifically, no hepatic cirrhosis was observed.
However, following an epidemic of pneumonia in the rat colonies, there
were 30 tumors in 73 animals in the selenate group, but only 20 in 75
animals in the controls.
Antitumorigenic Effects. A large accumulation of evidence indicates
that supplementation of the diet or drinking water with selenium protects
against tumors induced by a variety of chemical carcinogens and at least
one viral agent (Table 10-1). Although most investigators found that
tumor incidence in the selenium-supplemented animals was approximately
one-half that of the control animals, Schrauzer et_ al_. (1978) reported
that spontaneous breast tumors in female C3H mice were reduced from 82%
in controls to 10% in the selenium-supplemented animals. In all but two
of the experiments, comparisons were made between controls receiving
diets with nutritionally adequate selenium levels and test animals fed
diets supplemented with selenium levels 20 to 50 times higher than the
animal's requirements. In the remaining two experiments, Harr et al
(1972) and Ip and Sinha (1981) used selenium-deficient diets and demon-
strated beneficial effects of selenium supplementation at levels close to
the physiological requirement. Of special nutritional importance is
their finding that the incidence of tumors induced by 7,12-dimethyl-
benz[aj anthracene (DMBA) was enhanced by diets high in polyunsaturated
fatty acids and by dietary deficiency of selenium. Supplementation with
physiological levels of selenium (0.1 pg/g diet) resulted in protection
against tumor formation (Ip and Sinha, 1981).
10-5
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10-6
Although these data indicate that selenium has an antitumorigenic
effect, they provide no information on the mechanism of action or on the
stage of tumor development during which selenium might exert its protec-
tive action. In at least two studies, selenium was introduced only after
the carcinogen was applied and led to a reduction in tumor incidence.
Schrauzer ^t al* (1978) stated that the selenium levels in the recipient
animals do not influence the fate of transplanted tumor cells; others
observed a strong reduction in the growth of inoculated Ehrlich ascites
cells in recipient animals injected with high doses of selenium compounds
for 3 weeks after the inoculation (Greeder and Milner, 1980).
Mutagenicity. In vitro studies have not shed much light on the
mechanisms of action of selenium. On the one hand, selenium concentra-
tions from 0.1 to 40 mM exert antimutagenic effects against a variety of
mutagens in vitro, including the naturally occurring mutagen malonal-
dehyde (Jacobs et_ al . , 1977; Shamberger et^ al. , 1978). On the other
hand, similar concentrations of selenium have been reported to increase
DNA fragmentation and chromosome aberrations in human and microbial cell
cultures (Lo !* 1978; Nakamuro e al. , 1976). These contrasting
reports cannot be reconciled.
Potential Mechanisms of Action. There are data suggesting that
selenium in vitro and in vivo may decrease the activity of hydrox-
ylating enzymes that activate procarcinogens and may increase a detoxi-
fying enzyme glucuronyl transferase (Griffin, 1979). These results
suggest that selenium acts during the early stages of initiation.
The best known functions of selenium at nutritionally adequate,
but not at excessive, levels are its role as a part of the enzyme glu-
tathione peroxidase and its interaction with heavy metals. Glutathione
peroxidase destroys hydroperoxides and lipoperoxides, thereby protecting
the constituents of the cells against free radical damage. Ip and Sinha
(1981) have shown that selenium, through its function in glutathione
peroxidase, 'could well be involved in protecting against cancer induced
by high intakes of fat, especially polyunsaturated fatty acids. Gluta-
thione peroxidase activity in human blood increases with increasing
selenium intakes, but reaches a plateau at intakes well below those
customary in the United States (Thomson and Robinson, 1980). Thus, if
the antitumorigenic effect of selenium is mediated through its function
in glutathione peroxidase, attempts to increase the enzyme activity by
selenium supplementation, superimposed on an adequate diet in the United
States, would not be successful.
The second function of selenium is to protect against acute and
chronic toxicity of certain heavy metals. Although selenium is known to
interact with cadmium and mercury, the mechanism of action is not known.
Selenium does not cause an increased elimination of the toxic elements,
but, rather, an increased accumulation in some nontoxlc form (National
Academy of Sciences, 1971). It is conceivable that carcinogenic effects
of these, and perhaps other heavy metals, could be counteracted by
selenium, in a manner similar to its protection against their general
toxicity.
10-7
Summary
Epidemiological Evidence* The epidemiological evidence pertaining
to the relationship between selenium and cancer is derived from a limited
number of geographical correlation studies in which the risk of cancer
was correlated with estimates of per capita selenium intake, with the
selenium levels in blood specimens, or with selenium concentrations in
water supplies. Although these studies generally demonstrated an in-
verse relationship between the level of selenium and the risk of cancer,
it is not clear whether this relationship applies to all cancer sites or
only to specific cancer sites, such as those in the gastrointestinal
tract. There are as yet no data from case-control or cohort studies.
Experimental Studies. Numerous experiments in animals have demon-
strated an antitumorigenic effect of selenium. The relevance of most
of these studies to the risk of cancer for humans is not apparent since
the levels of selenium used far exceeded dietary requirements and often
bordered on levels that might be toxic. However, one experiment has
demonstrated increased susceptibility to DMBA-induced tumors when se-
lenium deficiency was aggravated by high dietary levels of polyunsatu-
rated fatty acids, and protection by a physiological supplement of se-
lenium (0.1 yg/g) to the diet (Ip and Sinha, 1981). The interpretation
of these results is further complicated because of the varied protocols
used in these experiments and the knowledge that selenium interacts with
many other nutrients, such as heavy metals in the diet.
The minimum requirement for selenium in mammalian species is 0.05
yg/g of diet, one-hundredth of the levels used in many studies of car-
cinogenesis. A level of 4 or 5 yg/g may not be acutely or even chroni-
cally toxic when fed along with a well-balanced, nutritious diet, but it
becomes chronically toxic when the quality of the diet is lowered, for
example when the protein content is reduced. At least two experiments
have demonstrated that selenium deficiency enhances carcinogenesis and
that physiological amounts of selenium have a significant protective
effect. The effectiveness of doses in the wide range between the
nutritionally adequate and the higher, effective level used in many
antitumorigenic studies has not yet been adequately Investigated. The
data on the mutagenicity of selenium compounds are also contradictory.
However, these experiments provide sufficient evidence to suggest that
the antitumorigenic effect of selenium should be investigated further.
Recent data do not support the earlier reports that selenium per se is
carcinogenic.
Conclusion
Both the epidemiological and laboratory studies suggest that
selenium may offer some protection against the risk of cancer. However,
firm conclusions cannot be drawn on the basis of the present limited
evidence. Increasing the selenium intake to more than 200 yg/day (the
10-8
upper limit of the range of Safe and Adequate Daily Dietary Intakes
published in the Recommended Dietary Allowances [National Academy of
Sciences, 1980b ] fbyThe use of supplements has not been shown to con-
fer health benefits exceeding those derived from the consumption of a
balanced diet.
ZINC
Zinc is an essential constituent of more than 100 enzymes and is
essential for life. Through its function in nucleic acid polymerases,
zincplays a predominant role in nucleic acid metabolism, cell replica-
tion, tissue repair, and growth (Prasad, 1978). Severe zinc deficiency
in humans has been known for 20 years; more moderate forms have been
linked to protein-energy malnutrition. Marginal zinc deficiency is
suspected to occur in a substantial number of infants and older children
in the United States (Prasad, 1978).
Pronounced zinc deficiency in animals and humans results in depressed
immune functions. Both tissue-mediated and humoral responses are
affected. Golden et al. (1978) have observed that impairment of delayed
hypersensitivity relcHons to Candida albicans antigen in malnourished
children can be normalized by topically applied zinc preparations, but it
is not known whether or to what degree immunocompetence is impaired
by marginal zinc deficiency.
Epidemiological Evidence
There have been few epidemiological studies of the relationship
between exposure to zinc and risk of cancer. Stocks and Davies (1964)
correlated cancer mortality with the zinc and copper content of soil in
12 districts of England and Wales. They found higher zinc levels and
higher ratios of zinc to copper in the soil of vegetable gardens near
houses in which a death from gastric cancer had occurred than in the soli
of gardens near houses in which there was a death attributed to another
cause. The levels near houses with deaths from "other cancers" did not
differ from those of the noncancer households. These analyses were made
only when the deceased had resided in the same house for 10 or more
years. Since the copper levels in soil varied little, the differences
could be attributed to zinc.
Schrauzer et al. (1977a,b) examined per capita food intake data in 27
countries. They found a direct correlation between estimated zinc intake
and age-adjusted mortality from leukemia and cancers of the intestine,
breast, prostate, and skin. Based on these findings and the inverse
correlation between zinc and selenium concentrations t blood, they
suggested that zinc increases cancer risk by its amtagonisp of selenium.
Van Rensburg (1981) observed that wheat and cor a*e the primary
dietary staples in many populations at high risk for esophageal cancer
10-9
around the world. In contrast, the staples in low-risk populations
include millet, cassava, yams, and peanuts. Since diets based on wheat
and corn generally contain low concentrations of zinc, magnesium,
nicotinic acid, and possibly riboflavin, he suggested that a deficiency
of one or more of these micronutrients might be etiologically related to
esophageal cancer.
A number of investigators have examined the relationship between
cancer and levels of zinc in blood and other body tissues. Schrauzer et_
al. (1977b) found that mean zinc concentrations in pooled blood from
healthy donors in 19 U.S. collection sites correlated directly with
corresponding mortality rates from cancers of the large bowel, breast,
ovary, lung, bladder, and oral cavity. Zinc and selenium levels in the
blood were inversely correlated with each other. Strain et_ ad . (1972)
compared zinc and copper levels in the serum of patients with broncho-
genie carcinoma and the levels in the serum of controls. Although zinc
levels did not differ between the two groups, the copper levels were
lower in the controls, resulting in higher ratios of zinc to copper in
the cancer patients. On the other hand, Davies e a]U (1968) reported
that zinc levels in the plasma of bronchogenic carcinoma patients were
lower than those of other cancer patients and lower than normal labora-
tory values.
Lin let^ aJU (1977) examined serum, hair, and tissues from Chinese men
in Hong Kong for levels of zinc and other minerals. They found that
levels of zinc in serum and diseased esophageal tissue from esophageal
cancer patients were much lower than those in other cancer patients and
in normal subjects. Zinc levels in hair were lower in both cancer groups
than in normal subjects. The serum of esophageal cancer patients also
contained slightly elevated copper levels and much lower iron levels
than the serum of normal subjects. Gytfrkey et_ a^. (1967) reported that
zinc concentrations in malignant prostatic tissue were lower than those
in normal tissue, whereas benign hypertrophied prostatic tissue contained
higher zinc levels. In all of these studies, the altered zinc levels
may have followed, rather than preceded, the onset of the cancers.
Experimental Evidence
Experiments in animals have demonstrated both enhancing and retarding
effects of zinc on tumor growth. Several reports suggest that a zinc
deficiency strongly inhibits the growth of transplanted tumors in animals
and prolongs survival time. The studies by Petering &!_ (1967) with
transplanted Walker 256 carcinoma in rats were confirmed by DeWys et al.
(1970) and extended to other types of tumors, such as leukemias, Lewis
lung carcinoma (DeWys and lories, 1972), Ehrlich ascites tumor (Bairr
and Harris, 1973), P388 leukemia (Minkel e al. . , 1979), and plasmacy-
toma TEPC-183 (Fenton e al. , 1980). The results of these studies are
consistent with the knowledge that rapidly growing tumor bells require
zinc for growth; however, they do not suggest zinc deficiency as a
therapeutic modality because zinc deficiency by itself, with or with-
out concomitant malignancies, results in death of the animals *
10-10
The results of these studies contradict reports indicating that zinc
deficiency enhances chemically induced carcinogenesis. For example, Fong
et al. (1978) observed that the incidence of esophageal tumors induced by
nitrosomethylbenzylamine (NMBA) was significantly higher in zinc-defi-
cient rats than in control rats. The intragastric intubation of NMBA in
a dose of 48 ug/g body weight resulted in a 15% incidence of carcinoma in
control rats fed ad libitum and a 43% incidence in rats maintained on
zinc-deficient diets. In two consecutive experiments, lowering the dose
of NMBA to 34 ]ig/g body weight produced no cancer in the control rats,
but 83% and 33% in the zinc-deficient animals. In contrast, some studies
have indicated that zinc intake greatly exceeding nutritional requirements
suppresses carcinogenesis induced by DMBA in Syrian hamsters (Poswillo
and Cohen, 1971) or by azo dyes in rats (Duncan and Dreosti, 1975). But
Schrauzer (1979) demonstrated that high concentrations of zinc (200 mg/
liter) in the drinking water of C3H mice countered the protective effect
of selenium against spontaneous mammary carcinoma and resulted in a
significant increase in tumor growth.
These contradictory reports are not easily reconciled. Perhaps there
are two different mechanisms of action by which zinc influences two dif-
ferent phases of carcinogenesis: Zinc, perhaps through its effect on the
immune system, may be protective during the early phases of transforma-
tion, whereas the demonstrated role of zinc in cell proliferation may
explain the protective effect of zinc deficiency against the growth of
established tumors. Furthermore, numerous interactions of zinc with
other trace elements, such as selenium, are incompletely understood.
Thus, the evidence is insufficient to determine the answer to an impor-
tant question: Does marginal zinc deficiency, believed to be widespread,
especially among children, present a risk for or provide protection
against carcinogenesis?
Summary
Epidemiological Evidence. There are few epidemiological data con-
cerning dietary zinc and cancer. Some studies have suggested that higher
levels of dietary zinc are associated with an increase in the incidence
of cancer at several different sites, including the breast and stomach,
and other studies have reported lower levels of zinc in the serum and
tissue of patients with esophageal, bronchogenic , and other cancers,
compared to corresponding levels in controls. However, the possibility
that the lower serum and tissue levels resulted from the cancer itself
has not been ruled out.
Experimental Evidence. Experiments in animals have shown that zinc
can either enhance or retard the growth of tumors. Zinc deficiency
appears to retard the growth of transplanted tumors, whereas it enhances
the incidence of some chemically induced cancers. In some experiments,
dietary zinc exceeding nutritional requirements has been shown to sup-
press chemically induced tumors in rats and hamsters, but when given in
10-11
drinking water it counteracts the protective effect of selenium in mice-
These data are insufficient to explain the effects of zinc and of inter-
actions between zinc and other minerals on tumorigenesis.
Conclusion
The epidemiological evidence concerning zinc is too sparse and the
results of laboratory experiments too contradictory to permit any con-
clusion to be drawn. In view of the important nutritional role of zinc
and of its many interactions with other minerals involved in carcino-
genesis, additional research is warranted to resolve the contradictory
results.
IRON
Epidemiological Evidence
Iron deficiency has been associated with cancers of the upper ali-
mentary tract including the esophagus and stomach. In epidemiological
studies conducted in Sweden, iron deficiency was associated with
Plummer-Vinson (Pater son-Kelly) syndrome, which in turn was associated
with increased risk for cancer of the upper alimentary tract (Larsson et
al., 1975; Wynder et^ al. , 1957). Improved nutrition, especially with
regard to iron and vitamins in the diet, has been associated with the
virtual elimination of new cases of Plummer-Vinson disease in areas of
Sweden where it had formerly been highly endemic (Larsson e aJ^. , 1975).
Broitman et al. (1981) studied iron-deficient patients with ante-
cedent lesions of gastric carcinoma in an area of Colombia with high
risk for this cancer. They found that hypochlorhydria and achlorhydria,
which are associated with chrdnic atrophic gastritis resulting from iron
deficiency, permitted bacterial colonization of the stomach. The investi-
gators postulated that these bacteria could reduce ingested nitrate to
nitrite, leading to the formation of nitrosamines that are carcinogenic
in the stomach of laboratory animals, and are suspected of being carcin-
ogenic in humans. A similar mechanism was suggested by Ruddell et al.
(1978) to explain the increased risk of gastric cancer in patients with
pernicious anemia.
There have been no epidemiological reports of cancer associated with
increased dietary intake of iron, although heavy inhalation exposure to
high levels of iron oxide has been related to increased risk for lung and
laryngeal cancers in miners of iron ore, metal workers, and workers in
iron foundries (Cole and Goldman, 1975). In addition, sarcomata have
developed in patients at sites of injection of iron-dextran solutions
(MacKinnon and Bane ewicz, 1973; Robinson et_ auU , 1960), and many clinical
reports have associated hemochromatosis with an increased risk for
10-12
hepatomas and possibly other hepatic and extrahepatic cancers (Armann et_
al. , 1980; Scott and Theologides, 1974; Steinherz et a!L. , 1976; Sussman
et al., 1974).
Experimental Evidence
Mild iron deficiency appeared to protect mice from the hepatocellu-
lar and porphyric toxicity due to 2, 3,7,8-tetrachlorodibenzo--dioxin
(TCDD) (Sweeney t. al. , 1979). It is not known if such protection might
extend to the teratogenic or possible carcinogenic action of TCDD. Rats
made severely deficient in iron through manipulation of their diet became
anemic and developed fatty livers (Vitale e aJU , 1978), but they were
devoid of any neoplastic lesions. However, in the same study, iron-
deficient rats given 1,2-dimethylhydrazine developed neoplastic lesions
in their livers within 4 months, as compared to 6 months in the iron-
sufficient group. The authors concluded that severe lack of iron
appeared to function as a cocarcinogen (Vitale jil i 1978).
Brusick et al. (1976) found that Fe(II) as iron sulfate induced
reverse mutatTons in Salmonella typhimurium strains TA1537 and TA1538
with the S9 fraction of various species. Weak.mutagenic activity was
also observed in nonactivated suspensions.
Summary
Epidemiological Evidence. Iron deficiency has been related to an
increase in the risk of Plummer-Vinson syndrome, which is associated
with upper alimentary tract cancer. Some evidence suggests that iron
deficiency may be related to gastric cancer, also through an Indirect
mechanism. Although epidemiological and clinical reports have suggested
that heavy exposure to iron by inhalation increases the risk of cancer,
there is no evidence pertaining to the effect of high levels of dietary
iron on the risk of cancer in humans.
Experimental Evidence. The evidence from experiments in animals is
limited. In one study, dietary deficiency of iron was associated with
an earlier onset of chemically induced tumors in rats. These data are
not sufficient to clarify the role of iron in carcinogenesis.
Conclusion
The data are not sufficient for a firm conclusion to be drawn about
the role of iron in carcinogenesis.
COPPER
Copper is an essential nutrient that is widely distributed in foods.
Public water supplies may be an additional source of copper. The intake
10-13
of copper In 28 countries has been reported by Schrauzer et a 1 * (1977b)
to vary between 1.6 and 3.3 mg/day. However, more recent studies indi-
cate that the average copper intake for U.S. adults is ^1 mg/day (Holden
et^a^., 1979; Klevay e al . , 1979).
Epidemiological Evidence
Schrauzer e al. (1977b) used pooled blood samples from healthy
donors in 19 U.S. states to correlate blood levels of copper with
corresponding cancer mortality rates. They found weak direct associa-
tions for cancers of the intestine, breast, lung, and thyroid. From
reported average concentrations of copper in major food items and inter-
national food disappearance data, they were also able to correlate per
capita intake of copper with cancer mortality rates in 27 countries. In
this portion of their study, they found direct associations for leukemia
and cancers of the intestine, breast, and skin. These investigators
proposed that the mechanism for the apparent carcinogenicity of copper
might involve selenium antagonism, since large doses of copper produce
symptoms of selenium deficiency in animals (Jensen, 1975).
The possibility that dietary exposure to copper, through the copper
content of either foods or cookware, may play an etlologic role in gas-
tric cajrcinogenesis is raised by the experiments of Endo e^ al. (1977),
who found that the copper ion may be Involved in conversion of creatine
and creatinine to methylguanidlne, a precursor of methylnitrosoguanidine.
However, no epidemiological data on the relationship of gastric cancer
and dietary copper have been reported.
In a number of clinical studies, levels of copper In the serum and
tissues of cancer patients were found to be higher than normal labora-
tory values and higher than levels in healthy subjects or in noncancerous
tissues (Schwartz, 1975). However, the possibility that these levels are
the consequence, rather than the cause, of the disease cannot be ruled
out. Indeed, many of these reports indicate that changes in copper levels
may be effected by therapy or by different stages and activity of the
disease.
Inhalation of copper has been suggested as a possible cause of
hepatic angiosarcoma as well as pulmonary adenocarcinoma and alveolar
cell carcinoma in workers who sprayed vineyards with a fungicide called
the Bordeaux mixture (coppet sulfate plus lime) (PImentel and Menezes^
1977). An increased risk for bronchogenic carcinoma has also been
reported for copper miners in cases Where exposure to radiation was
dismissed as a likely cause (Newman e al^. , 1976).
Thus, although some data suggest that copper is carcinogenic in
humans, very little epidemiological evidence implicates dietary sources
per se.
10-14
Experimental Evidence
Several independent studies have demonstrated that high levels of
copper salts added to the diets of animals provided various degrees of
protection against chemically induced liver tumors. The effects ranged
from a prolongation of the induction time to partial or complete protec-
tion against tumor formation. These studies, in which a variety of
different carcinogens were used, have been reviewed by Brada and Altman
(1978). Since these effects were obtained with extremely high concentra-
tions of copper (from 0.3% to 0.6% copper acetate in the diet) and since
similar effects have been produced when manganese or nickel were sub-
stituted for copper (Yamane and Sakai, 1973), the action of copper may
be pharmacologic , perhaps toxic in nature and nonspecific. There is no
experimental evidence that the copper levels in animal tissues influence
their susceptibility to carcinogens.
Summary
Epidemiological Evidence. Although there are some data from clinical
and epidemiological studies concerning the association of copper with
neoplasia in humans, there is little evidence pertaining to the role of
dietary copper in the etiology of human cancer.
Experimental Evidence . Experiments in animals have indicated that
pharmacological doses of copper appear to protect against chemically
induced tumors, but there are no studies to indicate whether the nutri-
tional copper status of animals influences their susceptibility to cancer*
Conclusion
The evidence does not permit any conclusion to be drawn about the role
of dietary copper in carcinogenesis.
IODINE
Iodine is an essential micronutrient in the diet and is an integral
component of thyroid hormones. Dietary deficiency of iodine is
associated with enlargement of the thyroid gland and endemic goiter, but
this does not occur commonly in the United States.
The mean daily intake of iodine in the United States is estimated to
range from approximately 60 to 680 yg/day. Even the lower level is
adequate to meet the minimum daily requirements of 50 yg, and many diets
furnish iodine in excess of the Recommended Dietary Allowance of 150 yg
(Fisher and Carr, 1974). The iodization of table salt, the use of iodine
in disinfectants, and the addition of iodate to dough conditioners have
contributed to the drastic reduction in iodine deficiency in the United
States. Together, these sources can also result in high intakes of
iodine, which are considered excessive by some nutritionists.
10-15
Epidemiological Evidence
Wahner et al. (1966) concluded that thyroid cancer occurred more
frequently I^*Cali, Colombia (an area of endemic goiter) than in New York
State or Puerto Rico. Their analysis was based on published data from
the United States and on a large autopsy series conducted by the authors
in Colombia. Although papillary carcinoma was the type of cancer found
most frequently in their series, the relative proportion of follicular
carcinomas was high compared with other areas of the world.
Williams e al . (1977) compared the incidence and histologic types of
thyroid cancer in two contrasting populations : Icelanders with high
iodide diets and Scots from northeast Scotland with normal levels of
dietary iodide. Based on a pathological review of all surgical thyroid
specimens in these areas, the investigators were able to determine the
histology-specific incidence rates of thyroid cancer. Their results
indicated that the incidence of papillary carcinoma and the ratio of
papillary to follicular carcinomas were higher in Iceland than in
Scotland. They concluded that high intake of iodide was associated only
with the papillary type of thyroid cancer, and suggested that low levels
of dietary iodide may increase the risk for follicular carcinoma of the
thyroid.
In studies that have not distinguished histologic types of thyroid
cancer, investigators have tended to find no associations with exposure
to iodine. Clements (1954) found no difference between observed and
expected deaths from thyroid cancer by state in Australia, despite the
fact that iodine intakes varied and endemic goiter was particularly
prevalent in Tasmania. Pendergrast t^ alU (1961) compared thyroid can-
cer mortality rates by state in the United States with corresponding
prevalence rates of endemic goiter and found no association between
the two diseases. They also examined secular trends in mortality from
these two diseases and observed that there had been a decline in endemic
goiter rates but not in thyroid cancer rates in the United States during
the previous 30-year period. Mortality data, used in both of these
studies, can be quite misleading for thyroid cancer and other cancers
that have very high survival rates.
A second type of cancer associated with iodine deficiency is breast
cancer in females. In an analysis similar to that of Pendergrast et al
(1961) for thyroid cancer, Bogardus and Finley (1961) compared mortality
rates for this cancer by state in the United States with the prevalence
of endemic goiter. They found a direct association between the two dis-
eases. Commenting on this observation, Stadel (1976) noted that breast
cancer in females is highly correlated with endometrial and ovarian
cancers and hypothesized that low iodine intake may be etiologically
related to all three cancers. However, the results of many other stud-
ies do not support this association. Edington (1976) reported conflict-
ing data obtained in sub-Saharan Africa, where these three cancers are
rare despite very low levels of dietary iodine. In Hawaii and Iceland >
iodine intake is high, but there are also high '/"incidence .rate's ^:for v
cancer (Waterhouse et al., 1976).
10-16
Experimental Evidence
Eskin et_ aJL . (1967) and Aquino and Eskin (1972) reported that iodine
deficiency produces hyperplastic changes in the breast tissue of female
rats during puberty. Because of the epidemiological correlations indi-
cating a higher incidence of mammary carcinoma in areas with endemic
goiter, Eskin (1978) studied the influence of iodine deficiency, per
se, on mammary tissue when the thyroid was maintained in a normal state.
Deficiency resulted in dysplastic changes of the epithelium, which were
aggravated by estrogen treatment and advanced to preneoplastic and neo-
plastic conditions. These changes were reversible by supplementation
with inorganic iodine but not thyroxine which, in higher doses, increased
the dysplastic changes. Eskin proposed that iodine deficiency Itself
rather than hypothyroidism was responsible for these effects and demon-
strated similar changes by blocking iodine uptake with perchlorate. Upon
termination of the blockade or dietary iodine supplementation, most but
not all of the hyperplastic tissue changes returned to normal. The
iodine-deficient prepubescent rats were also susceptible to earlier
appearance of DMBA-induced mammary tumors, suggesting a cocarcinogenic
effect of iodine deficiency.
Eskin et_ al . (1976) also demonstrated that the ratios of DNA to RNA
in the breast of iodine-deficient rats were much higher than those for
control rats. In addition, observed alterations in the estrogen receptor
protein may suggest that mammary tumorigenesis may be stimulated in the
presence of estrogen and higher physiological levels of its receptor, as
observed in iodine deficiency. Exposure of iodine-deficient animals to
a carcinogen such as 2-acetylaminofluorene (2-AAF) or to thyroid irra-
diation has been reported to result in increased yields of malignant
thyroid tumors (Bielchowsky , 1944; Doniach, 1958).
Summa r y
Epidemiological Evidence. Although studies that focused on mortality
from thyroid cancer showed no association of the disease with dietary
iodine, a large series of autopsies from Colombia and a study of cancer
incidence in Iceland and Scotland, based on histology-specific analyses,
suggested that the risk of follicular thyroid carcinoma may be increased
in iodine-deficient populations. In the Iceland/Scotland study, investi-
gators also found a higher incidence of papillary carcinoma in the popula-
tion with high dietary iodine intake. However, the relationship between
iodine and thyroid cancer should be studied further before firm conclu-
sions can be drawn. Epidemiological studies provide no clear evidence
that the risk of cancers of the breast, ovary, and endometrium are relate*
to dietary iodine deficiency.
Experimental Evidence. Experimentally ixiduceel iodine deficiency
seems to predispose rats to the development of pr^neoplfiLStic and neo-
plastic lesions in mammary tissue and to reduce the Induction time of
chemically induced mammary and thyroid
10-17
Conclusion
Although limited epidemiological and laboratory evidence suggests
that iodine deficiency is associated with an increased risk for thyroid
cancer in humans, the evidence is not conclusive.
MOLYBDENUM
Epidemiological Evidence
A few reports have indirectly implicated molybdenum deficiency in the
etiology of cancer, especially cancer of the esophagus. In China, the
Coordinating Group for Research on Etiology of Esophageal Cancer in North
China (1975) and Yang (1980) reported that correlation analyses by county
have shown an inverse association of esophageal cancer with the levels of
molybdenum and a variety of other minerals in the soil. Molybdenum levels
in hair were low in areas at high risk for this cancer. Low levels of
molybdenum in the soil have also been observed in a region of Africa with
high mortality rates from esophageal cancer (Burrell it a^. , 1966). Fur-
thermore, low levels of molybdenum in water supplies have been correlated
with excess esophageal cancer mortality in the United States (Berg et
al. , 1973).
In areas of China at high risk for esophageal cancer, supplementation
of the soil with ammonium molybdate has been observed to increase the
molybdenum and ascorbic acid content of locally produced grains and
vegetables and to decrease their nitrate and nitrite concentration (Luo
e al . , 1981). The investigators have proposed that high ascorbic acid
and decreased nitrate and nitrite content of vegetables and grains could
decrease the high incidence of esophageal cancer in these areas.
Experimental Evidence
Luo ej^ aim (1981) studied the effect of molybdenum supplementation on
the induction of tumors' by N-nitrososarcosine in the esophagus and fore-
stomach of Sprague-Dawley rats. They observed that tumor incidence in
the group supplemented with molybdenum (2 mg/ liter drinking water) was
lower than that in the control group, whose diet contained a molybdenum
concentration of 26 yg/kg diet.
Molybdenum ill the form of molybdenum oxide was shown to induce a
significant increase in the number of lung adenomas in Strain A mice
(Stoner et al., 1976). Molybdenum as potassium molybdate and ammonium
molybdate~waJ positive in Bacillus subtilus reo assay (Nishioka, 1975).
Nishioka (1975) also rioted the mutagenicity of ammonium molybdate in
Escherchia coli*
10-18
Summary
Epidemiological Evidence* In a few studies, investigators have
found an inverse correlation between molybdenum levels in the soil and
water and the risk of esophageal cancer, especially in China. Supple-
mentation of molybdenum-deficient soil in high risk areas of China has
been observed to increase the ascorbic acid content and lower the ni-
trate content of locally grown plants and grains, and is therefore being
considered as a means of reducing the risk of esophageal cancer.
Experimental Evidence. Data from one report of laboratory experi-
ments suggest that molybdenum supplementation of the diet may reduce the
incidence of nitrosamine-induced tumors of the esophagus and forestomach.
Conclusion
The epidemiological and laboratory evidence is too meager to assess
the validity of the associations suggested by the studies summarized
above
CADMIUM
Regarded only as a toxic substance for many years, cadmium is now
beginning to be recognized as an element with a possible physiological
function (Schwarz, 1977). Market Basket Surveys conducted by the Food
and Drug Administration indicate that the per capita intake of cadmium
in the United States ranged from 26 to 61 yg/day during 1968-1974
(Mahaffey et_ a]U , 1975). The tolerable weekly intake for cadmium
established by a FAO/WHO Expert Committee is from 400 to 500 yg/week
(World Health Organization, 1972).
Epidemiological Evidence
In a correlation analysis based on c&ncer mortality by state and
trace element content of the water supplies in 10 river basins of the
United States, Berg and Burbank (1972) found direct associations be-
tween cadmium levels and mortality from myeloma, lymphoma, and cancers
at several other sites, including the mouth and pharynx, the esophagus,
the large intestine, the larynx, the lung, the breast (female), and the
bladder. Four other trace elements (arsenic, beryllium, nickel, and
lead) were also directly associated with cancer, but chromium, cobalt,
and iron were not.
Schrauzer ejt al . (1977a,b) correlated estimated per capita cad-
mium intakes with cancer mortality rates in 27 countries. They found
significant direct associations with leukemia and cancers of the
intestine, female breast, uterus, prostate, and skin, and an inverse
10-19
association with liver cancer. A similar analysis, based on the cad-
mium concentration in pooled blood samples and cancer mortality in 19
U.S. states, yielded significant direct correlations for uterine cancer
and stomach cancer in females. Schrauzer and colleagues suggested that
cadmium may act as a selenium antagonist to prevent its uptake and lower
its physiological activity as an anticarcinogen.
Kolonel (1976) reported the results of a case-control study in which
the combined exposure to cadmium from three sources (diet, cigarette
smoking, and workplace) was associated with increased risk for renal
cancer. In studies based on occupational exposure (Adams et al., 1969;
Kipling and Waterhouse, 1967; Lemen et al. , 1976; Potts, 1"5>5"5T7
investigators have observed associations between exposure to cadmium and
prostate cancer. However, the main source of exposure to cadmium for the
general population is diet (Friberg et_ al., 1974), and a case-control
study of prostate cancer that included dietary as well as occupational
exposure (Kolonel and Winkelstein, 1977) failed to confirm this
association between cadmium and prostate cancer.
Experimental Evidence
Carcinogenici ty . Except for one long-term study In which Schroeder
et al. (1964, 1965) observed no carcinogenic effect in mice given cad-
mium at 5 mg/liter drinking water, no studies have been conducted in
laboratory animals to determine the effect of dietary cadmium on
carcinogenici ty.
Intramuscular injection of cadmium powder induced sarcomas in hooded
rats (Heath al,. , 1962). Subcutaneous injections of cadmium sulflde,
cadmium oxide, cadmium sulfate, or cadmium chloride induced sarcomas and
Leydig cell tumors in Wlstar rats of the Chester Beatty strain (Wl/Cbl)
(Haddow et_ al^. , 1964; Kazantzls and Hanbury, 1966; Roe et al. , 1964).
Intratestlcularly administered cadmium chloride also induced teratomas In
White Leghorn cockerels (Guthrie, 1964) and sarcomas in Wistar rats and
albino mice (Gunn t l. , 1963, 1964, 1967).
Mutagenicity and Related Tests. Sirover and Loeb (1976) found that
various salts of cadmium decreased the fidelity of avian myeloblastosis
virus (AMV)/DNA polymerase for replication of synthetic polynucleotide
templates. Cadmium salts were mutagenic to Escherichia coll (Yagi and
Nishioka, 1977) and positive in rec assay in Bacillus subtilis (Nishioka,
1975). Shiralshi et al . (1972) found that in vitro treatment of human
lymphocytes with cadmium sulfide induced chromosome aberrations. Casto
t al * '(1976) reported that cadmium (II) Induced the formation of morpho-
logically altered colonies In Syrian hamster fetal cells.
Summary
Epidemiological Evidence. The effect of dietary cadmium on cancer
has been examined in only a few epidemiological studies. The results of
10-20
three studies suggested that Ingestion of cadmium in food or drinking
water is associated with an increased risk of cancer, but another study
did not confirm these findings. Occupational exposure to cadmium has
been associated with an increase in the risk of renal and prostate cancer.
Experimental Evidence* Data from one laboratory experiment suggest
that cadmium given in drinking water is not carcinogenic in mice, whereas
intramuscular and subcutaneous injections of cadmium salts induce cancer
in rats and mice. Some salts of cadmium induce mutations in bacteria and
chromosome aberrations in human lymphocytes in culture. The implications
of the latter findings for the effect of dietary exposure to cadmium are
not clear.
Conclusion
The evidence from epidemiological and laboratory studies does not
permit any firm conclusions to be drawn about the effects of dietary
exposure to cadmium.
ARSENIC
Arsenic is considered to be an essential element for growth in
animals (Schwarz, 1977). Small amounts of this element are widely dis-
tributed throughout the soils and waters of the world, and trace amounts
occur in foods (especially seafood) and in some meats and vegetables.
Arsenic may be present in food as a contaminant or as the unintentional
residue of calcium arsenate or lead arsenate, which are used as insecti-
cides, particularly on fruits and potatoes. A Market Basket Survey of 28
cities conducted by the Food and Drug Administration (FDA) during 1969-
1970 revealed that arsenic levels in dairy products were less than 0.1
mg/kg, but ranged from 0.1 to 2.6 mg/kg in meat, fish, and poultry
(Corneliussen, 1972). In the most recent published survey (for FY 1977),
arsenic was detected in 45 of 300 (15%) food composites in amounts rang-
ing between 0.02 and 0.83 mg/kg (U.S. Food and Drug Administration,
1980). In one study of selected trace elements in 727 samples of U.S.
surface waters, the concentration of arsenic ranged f rom < 10 to 1,100
]ig/liter (Durum et_ al. , 1971). In river waters, the median concentration
of arsenic was less than 10 pg/ liter. The daily intake of arsenic in the
United States was reported to average 63 pg/day between 1965 and 1970,
10 yg/day in 1973, and 21 ug/day in 1974 (Mahaffey ejt al . , 1975).
Because of the variations in individual susceptibility to the tox-
icity of arsenic and differences in toxicity of the various chemical
forms of arsenic, it is difficult to estimate the average tolerable level
for arsenic. No provisional tolerable daily intake has been established
for arsenic by the World Health Organization*
10-21
Epidemiological Evidence
Most of the epidemlological evidence for the carcinogenicity of
arsenic has been obtained in studies of lung cancer among workers
occupationally exposed to inorganic arsenic by inhalation. In addition,
several clinical reports have recorded observations of an unexpectedly
high frequency of skin cancer among patients treated with inorganic
arsenic drugs (e.g., Fowler's solution). Neither of these sources of
exposure is dietary.
Water supplies may contain arsenic, and the consumption of contami-
nated water has also been associated with an increased risk for skin
cancer in certain regions of the world. For example, studies in Taiwan
have shown a direct relationship between the arsenic content of well
water and the prevalence of skin cancer in the population drinking the
water (Tseng, 1977; Tseng et_ al. , 1968).
Epidemiological literature on cancer risk associated with occupa-
tional, medicinal, and drinking water sources of exposure to arsenic has
been reviewed in publications by the International Agency for Research
on Cancer (1973, 1980a) and the National Academy of Sciences (1977a,b;
1980a).
The occurrence of cancers of the skin, lung, and liver (hemangioendo-
theliomas) in association with clinical evidence of chronic arsenism has
been reported among vineyard workers in the Federal Republic of Germany
and in France (Galy et^ al. > 1963; Latarjet et^ alU , 1964; Roth, 1957a,b).
The workers had been exposed to arsenic both from inhalation of arsenical
pesticides and from ingestion of contaminated wine. These reports suggest
the possibility that a carcinogenic risk resulted from the ingestion of
the wine. On the other hand, Nelson et_ al^ (1973) found no increased
risk for total cancer mortality or for lung cancer specifically in a
cohort of residents in the State of Washington who had consumed apples
from orchards treated with lead ar senate sprays. (There was also no
increase among the workers who applied the sprays.) Moreover, ingestion
of arsenic-contaminated foods in Japan, including powdered milk and soy
sauce, has not been associated with any Increased occurrence of cancer
(Tsuchiya, 1977).
Experimental Evidence
Carcinogfenicity . Hueper . gini Payne (1962) exposed rats and C57BL mice
firom the age of 2 months to 15 mpntha to a 0*0004% solutioii of arsenic in
12% aqueous ethpnol through drinking water. The incidence of tumoirs In
the treated groiip was no greater than that in the untreated controls.
The tumor incidence in Swiss mice receiving 001% was similar to that of
the control mice (Baroni et al., 1963). In another study, Rockland all-
purpose mice fed potassiuraTarsenite at 169 ug/g diet for 48 weeks and
also exposed to this chemical by skin painting failed to develop more
tumors than did the control animals (Boutwell, 1963).
10-22
In rats exposed daily to 10 mg of lead arsenate or calcium arsenate
for 2 years, there was no increase in the incidence of tumors (Fairhall
and Miller, 1941). Byron et_ jaJU (1967) similarly reported no evidence of
carcinogenicity in a 2-year study in which Osborne-Mendel rats were fed
sodium arsenite (which provided arsenic at 0-250 jig/g diet) or sodium
arsenate (which provided arsenic at to 440 pg/g diet). In dogs, sodium
arsenite or sodium arsenate fed at levels of 5, 25, 50, and 125 pg/g diet
for 2 years produced no increase in the incidence of tumors (Byron et
al . , 1967).
Cocarc inogenicity * Arsenic has also been evaluated as a cocarcinogen,
but the results were negative when tested in combination with urethane,
DMBA, and N-nitrosodiethylamine (Furst, 1977).
Mutagenicity. Rossman e all. (1977) reported that sodium arsenite
significantly decreased the survival of wild type Escherichia coli (WP)
after irradiation, suggesting that it inhibits one or more steps in the
postreplication DNA repair pathways. Arsenic (III) yielded positive
results in Bacillus subtilis rec assay (Nishioka, 1975). It has also
been shown to transform Syrian hamster cells jin vitro and to enhance the
susceptibility of these cells to transformation by ^imian adenovirus
(Casto et l. , 1976).
Chromosome breakage in leukocytes of humans exposed to arsenic com-
pounds was reported by Petres and Berger (1972) and Petres and Hundeiker
(1968). Analysis of lymphocytes from exposed patients indicated that
frequent chromosome aberrations occurred even decades after the last
exposure (Petres et al. , 1970, 1977). Paton and Allison (1972) reported
that sodium arsenite and acetylarsan induced chromosome aberrations in
diploid fibroblasts of humans.
Nordenson et al. (1978) reported that exposure to arsenic com-
bined with cigarette smoking significantly enhanced the incidence of
chromosome aberrations in the lymphocytes of smelter workers, compared
to the incidence for nonsmoking smelter workers exposed to arsenic
alone. The authors speculated that the chromosome aberrations may have
been initiated by smoking or by some other agent in the workplace en-
vironment, and that exposure to arsenic may have inhibited their repair.
Summary and Conclusions
Arsenic is unique among the various agents covered in this report in
that it has been associated with cancer in humans but not in laboratory
animals.
Epidemiological Evidence. There is good evidence that drinking water
heavily contaminated with arsenic increases the risk of skin cancer in
humans in some parts of the world, and some evidence that the risk of
lung cancer is increased by inhaling arsenic in occupational settings.
10-23
However, the reported epidemiological studies do not provide sufficient
information to determine the effects of the normally low levels of
dietary arsenic on cancer risk.
Experimental Evidence* Arsenic does not appear to induce tumors in
laboratory animals despite extensive testing in animals of various spe-
cies. It is possible that humans are more sensitive to the carcinogenic
effects of arsenic and that the appropriate animal species, strain,
dosage schedule, compound, or the route of exposure have not yet been
identified.
LEAP
Although a requirement for trace amounts of lead (29 ng/g diet) has
recently been demonstrated in rats for the maintenance of growth,
reproduction, and heraopoiesis (Relchlmayr-Lais and Kirchgessner, 1981),
it is not known to be essential to human nutrition. Humans are exposed
to oxides and salts of lead through various environmental sources such as
automobile exhausts, atmospheric dust, drinking water, food, and paint,
all of which contribute to the total body burden of lead. The dietary
intake of lead in the United States was estimated to be 60 lag/person/day
in 1973 and 19 ]ig/day in 1974 (Mahaffey et al., 1975).
Epidemiological Evidence
Berg and Burbank (1972) correlated the levels of eight trace ele-
ments in the water supplies of 10 major river basins in the United States
with corresponding cancer mortality rates for white and nonwhite males
and females. There were significant correlations for five of the eight
elements. Among these was lead, which was directly correlated with
cancers of the stomach, small Intestine, large Intestine, ovary, and
kidney, as well as with myeloma, all lymphomas, and all leukemias.
Nelson e_t_ al^. (1973) found no increased risk for cancer mortality in a
population that consumed apples from orchards treated with lead arsenate
spray; thus, neither lead nor arsenic in this form was implicated as a
carcinogen.
Occupational exposure to lead has not been conclusively associated
with any form of cancer. Most studies have shown no association
(Dingwall-Fordyce and Lane, 1963; Robinson, 1976), although the results
of the study by Cooper and Gaffey (1975) can be interpreted as either
demonstrating or not demonstrating a relationship, depending on the
method of analysis used (International Agency for Research on Cancer,
1980b; Kang et a!. > 1980).
Experimental Evidence
Ca re Inogeni ci ty The number of renal tumors that developed in Swiss
mice fed 0.1% lead subacetate was significantly higher than that observed
10-24
in untreated controls (Van Esch and Kroes, 1969). There were also signif-
icantly more renal tumors in Wistar rats fed lead acetate, as compared to
controls (Mao and Molnar, 1967; Shakerin and Paloucek, 1965; Van Esch t
al., 1962; Zawirska and Medras, 1968). Lead nitrate and lead powder were
found not to be carcinogenic when fed to Long Evans and Fischer rats,
respectively (Furst et_ al . , 1976; Schroeder e al . , 1970). In several
other feeding studies, the majority of rats developed renal tumors;
however, these studies did not include concurrent untreated control
animals (Boyland et_ al. , 1962; Hass et_ al. , 1967; Ito, 1973; Ito et al.,
1971).
Mutagenicity. Lead (II) reacted with phosphate groups of DNA bases
to yield stable complexes (Venugopal and Luckey, 1978; Sissoeff et al.,
1976). Sirover and Loeb (1976) reported that 4 mM lead chloride
diminished the fidelity of DNA polymerase.
Lead acetate was found to be negative in the Ames test and E. coli
pol A assay for DNA-modifying effects (Rosenkranz and Poirier, T979);
in the host-mediated assay in Swiss Webster mice with Ames Salmonella
strains and Saccharomyces cerevisiae D3 as indicator organisms (Simmon
et al., 1979); in the mitotic recombination assay with Saccharomyces
cerevisiae D3 (Simmon, 1979); and in the Bacillus subtilis rec assay
(Kada et al. , 1980; Nishioka, 1975).
Bone marrow cells from rats treated with 1% lead acetate in drinking
water had more chromatid gaps, fragments, deletions, and translocations
than did the same cells from controls (Teodorescu and Calugaru, 1972).
i
Bauchinger and Schmid (1972) reported that there were more achromatic
lesions in Chinese hamster ovary cells treated with 1 mM lead acetate
than in untreated controls. Morphological transformations of Syrian
hamster embryo cells were observed after exposure to lead acetate (1-2.5
g/liter medium), which produced fibrosarcomas in Syrian hamsters (DiPaolo
et ail., 1978).
Lead acetate (10"^ mM) induced achromatic lesions and chromatid
and isochromatid breaks (Beek and Obe, 1974), but not sister chromatid
exchanges in leukocytes from humans (Beek and Obe, 1975).
Summary
Epidemiological Evidence. There is very little epidemiological
evidence linking dietary lead to the risk of cancer in humans. The only
study that correlated lead levels in drinking water supplies and cancer
mortality suggested that lead increased the risk of cancer. Exposure to
lead in industrial settings has not been clearly associated with an
increased risk for any form of cancer.
Experimental Evidence. The ingestion of higE levels of lead
compounds induces renal tumors in mice and rats.
10-25
Conclusion
On the basis of experiments in animals, it would seem that exposure
to large amounts of some compounds of lead may pose a carcinogenic risk
to humans. However, there is little direct epidemiological evidence to
support this conclusion.
10-26
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Cancer Res. 40:2633-2644.
Zawirska, B., and K. MedraS. 1968. [In German.] Tumoren und St*Jr-
ungen des Porphyrinstof fweschels bei Ratten mit chronischer experi-
menteller Bleiintoxikation. Zentralbl. Allg. Pathol. Pathol. Anat.
111:1-12.
CHAPTER 11
ALCOHOL
Estimates f o per capita alcoholic beverage intake based on taxes
paid on alcohol purchases in various countries may be moderately or
extremely low. This is partly because alcoholic beverages purchased
either illegally or by special sanctions from U.S. government agencies
escape taxation, and thus, inclusion in the tax records from which the
estimates are drawn. Studies based on surveys are also prone to error
because consumers tend to underestimate their alcohol intake (DeLuca,
1981).
EPIDEMIOLOG1CAL EVIDENCE
Specific Alcoholic Beverages
A number of reports implicate specific alcoholic beverages as risk
factors for cancers at certain sites. Using data on per capita intake
of various types of alcoholic beverages and standard mortality ratios
in the 46 prefectures of Japan, Kono and Ikeda (1979) found only
suggestive correlations for males between cancer of the esophagus and
intake of botfh Whiskey and shochu; cancer of the rectum and wine intake;
and .cancer of the prostate and shocbu intake. There were no correlations
for females. Cook (1971) and Gollis al_. (1972) ascribed the high
frequency of esophageal cancer in an African population to the consump-
tion of an alcoholic beverage prepared from maize. In the Normandy
region of J*catice, people who consumed home-distilled apple brandy had
an increased risk of 4sophageal eancer, compared to nondrinkers (Tuyns
t__al/, 1979). Smoking enhanced this risk (Tuyns and Masse, 1973; Tuyns
ejt_ e_l. , 1977)* In a very early study, Lamy (1910) reported an associa-
tion between esophageal cancer and the consumption of absinthe by chronic
alcoholics in France. In China, where earlier records indicated that
esophageal cati&er icoutprised approximately one-half of the gastrointesti-
nal tract cancers, pai-kan, a strong alcoholic beverage, was cited as an
etiological agent (Kwati, J 1937,; Wu and Loucks, 1951).
Recently* Hoey et al . (1981) reported ttiat the consumption of alcohol
(primarily red wineTlLncreased the risk of adenocarcinoma of the stomach.
In this study, wtidbch was conducted in Lyon, France, patients with gastric
cancer consumed approximately 800 calories per day as alcohol compared to
400 calories per day for patients with other digestive
In a multi-ethnic population living in Hawaii, a direct association
was observed for beer consumption and eight cancer sites (including
tongue/mouth, pharynx, larynx, esophagus, stomach, pancreas, lung, and
kidney) (Hinds e al^. , 1980). In the mainland United States, Breslow and
Enstrom (1974) and Enstrom (1977) demonstrated a statistically signifi-
carit association between per capita beer intake and colorectal cancer,
11-2
especially rectal cancer. Wynder and Shigematsu (1967) reported that a
group of 314 male colorectal cancer patients contained a significantly
higher proportion of beer drinkers than did one control group, but there
were no differences between the cases and a second control group. In a
study of 166 male bowel cancer patients in Great Britain, Stocks (1957)
demonstrated a significant association with beer drinking. Bjelke (1973)
reported a dose-response relationship for the risk of colorectal cancer
and the frequency of beer and liquor consumption in a prospective study
of 12,000 middle-aged Norwegian men. Dean e al. (1979) also reported a
direct association based on a cohort study in Dublin. Conversely, case-
control studies of bowel cancer in Finland, Kansas, and Norway by Pernu
(I960), Higginson (1966), and Bjelke (1971, 1973) showed no significant
relationship with beer drinking. Similarly, no associations were ob-
served in a correlational analysis by Hinds e al. (1980) or in a cohort
study by Jensen (1979).
Using international data and estimates of ethanol intake from beer,
wine, and distilled spirits, Vitale et^ a.1 . (1981) demonstrated a corre-
lation coefficient of 0.78 for beer drinking and colorectal cancer in 20
countries. Poor correlations were obtained for colon cancer and intake
of total ethanol, distilled spirits, or wine.
Thus, in certain populations throughout the world there appears to be
an association between consumption of strong, locally prepared alcoholic
beverages and esophageal cancer. There also appears to be a statistically
significant association between beer drinking and colorectal cancers in
certain countries but not in others. These associations with specific
beverage types suggest that the effects may be due to intake of other
contaminants in the beverages, rather than to consumption of ethanol per
se.
As noted above, epidemiological studies have linked the consumption
of alcoholic beverages to the development of cancers at various sites.
In an ideal study to examine this relationship, alcohol abusers and
"moderate" drinkers should be studied separately. In the abusers,
alcohol may play a modifying or contributing role in carcinogenesis by
inducing nutritional deficiency diseases that, in turn, may interact in
the process of carcinogenesis in the host. This effect of alcohol may be
different in moderate drinkers. However, because it is difficult to
determine alcohol intake with accuracy, the distinction between alcohol
abuse and moderate drinking in the studies described below is to some
extent arbitrary.
Total Alcoholic Beverages
An association between cancer at various sites and alcohol abuse has
been recognized for some time. In France, Piquet and Tison (1937)
observed that 95% of their patients with esophageal cancer were alcohol
abusers. In a study of 4,000 French patients, Schwartz and colleagues
11-3
showed a significant correlation between mean daily alcohol consumption
and frequency of cancers of the tongue, hypopharynx, and larynx (Schwartz,
1966; Schwartz et^ ad . , 1962, 1966). A large majority of the Individuals
with cancers at these sites were heavy drinkers. In a Finnish male cohort
study, chronic alcoholics were found to have excess morbidity from cancers
of the pharynx, esophagus, and lung (Hakulinen t al. , 1974). On the
basis of a literature survey, the World Health Organization (1964) con-
cluded that excessive consumption of alcoholic beverages was associated
with cancer of the mouth, larynx, and esophagus. Case-control studies
conducted in the United States have established that excessive consumption
of alcoholic beverages increases the risk of incurring cancer of the oral
cavity, excluding the lip, glottis and supraglottlc region, larynx, and
esophagus (Bross and Coombs, 1976; Burch e al. , 1981; Graham et al.,
1977; Kaminonkowski and Fleshier, 1965; Keller and Terris, 1965; Keller
et^ al. , 1977; Moore, 1965; Rothman and Keller, 1972; Schottenfeld, 1979;
Schottenfeld jat al . , 1974; Vincent and Marchetta, 1963; Wynder and Bross,
,1961; Wynder et_ al. , 1957a). Salient features of the earlier studies
have been summarized by Keller et al. (1977) in a report prepared for the
U.S. Congress.
Excessive alcohol consumption has also been linked with the develop-
ment of hepatomas (MacDonald, 1956). Purtllo and Gottlieb (1973) noted
that by far the greatest number of hepatomas were hepatocellular carcino-
mas, which were found in 72% of the hepatoma patients studied. Approxi-
mately one-half of the 98 patients In this series were alcohol abusers.
The investigators suggested that chronic alcoholism contributed to the
development of hepatomas by inducing cirrhosis. Keen and Martin (1971)
suggested that aflatoxin consumed by African patients induced hepatomas
indirectly by first inducing cirrhosis. Vogel and his associates (1970)
found hepatitis-associated antigen (HAA) in African patients with hepato-
mas. Hepatitis B antigenemia has been frequently associated with hepato-
cellular carcinomas ( Sherlock e a]U , 1970; Vogel et_ ail. , 1970; Wu and
Lam, 1979). In general, hepatomas are found In Individuals with cirrho-
sis. Thus, agents such as alcohol, hepatitis antigen, and aflatoxin,
which result in hepatic injury leading to cirrhosis, may contribute to
the development of hepatomas through this pathway. A number of etiolo-
gies have been proposed for the development of carcinomas through the
hepatocellular regeneration that accompanies cirrhosis (Lieber et al.,
1979).
There is a substantial amount of experimental evidence Indicating
that aflatoxin is a carcinogen as well as a hepatotoxin (Rogers and
Newberne, 1971), but there is no direct evidence that hepatitis B virus
is oncogenic. (See Chapter 12 for a discussion of primary liver cancer
associated with exposure to hepatitis B viral infection. ) No adequate
studies have been conducted to determine whether alcohol per se is
carcinogenic or cocarcinogenic in the develoment of hepatomas in the
absence of cirrhosis.
Lieber t al . (1979) reported that a small number of alcohol abu-
sers developed hepatocellular carcinomas in the absence of cirrhosis.
11-4
Although other investigators (e.g., Keller, 1978) reported similar
findings, Lieber and colleagues suggested that the numbers were too small
to ascertain if the tumor incidence was significantly greater in alcohol
abusers than in moderate drinkers or nondrinkers. Additional studies are
required to evaluate fully the role of ethanol in hepatocarclnogenesis.
Other sites in the digestive tract where cancer has also been asso-
ciated with alcohol abuse include the gastric cardia (MacDonald, 1972)
and the pancreas (Burch and Ansari, 1968).
Synergism Between Alcohol and Smoking
Alcohol consumers (especially abusers) are, more often than not,
smokers. Flamant et^ a^. (1964), assessing both variables, stressed the
interaction between alcohol consumption and smoking for cancers of the
oral cavity and the esophagus. Studies completed since then have con-
firmed these findings supporting an interactive role between tobacco and
alcohol in tumorigenesis of the oral cavity, the larynx, and esophagus
(Burch et^al., 1981; Keller and Terris, 1965; Martinez, 1970; Pottern et
al. , 1981, Rothman and Keller, 1972; Wapnick et a.1. , 1972). Avoidance of
tobacco and alcohol by males could effect a marked reduction of these
cancers (Rothman, 1980; Rothman and Keller, 1972). Flamant e_t_ al . (1964)
suggested that alcohol abuse may be more important than smoking in? the
development of esophageal cancer, but smoking is more closely allied to
cancers of the mouth and pharynx.
It is difficult to ascertain if moderate or heavy consumption of
alcohol (other than the beverages specified above) enhances the risk of
oral and upper respiratory tract cancer in nonsmokers. Synergistic
effects of alcohol and smoking have been observed in smokers consuming
45 ml or more of ethanol per day (Schottenf eld, 1979). Cancer sites
correlating with past ethanol consumption more strongly than with ex-
posure to tobacco include the floor of the mouth, supraglottic region,
hypopharynx, and esophagus (Omerovic, 1976; Spalajkovic, 1976; Stevens,
1979). Since alcohol consumption involves direct exposure of the sites,,
Kissin (1975) suggested that ethanol exerts a direct local effect rather
than a systemic one. Geographic, ethnic, and dietary factors may also be
of some consequence in esophageal cancer (Pothe and Voigtsberger, 1976;
Sadeghi et_ al. , 1977; Schwartz e al. , 1966; Steiner, 1956). A case-
control study conducted by Graham e aJ . (1977) introduced still another
variable. These investigators reported that the interaction of tobacco
and alcohol in cancers of the oral cavity was apparent only in individuals
with clinical evidence of inadequate dentition.
McCoy e al . (1979) noted that excessive ethanol consumption and
exposure to tobacco may act synergistically to affect the risk of cancer
of the upper alimentary and respiratory tracts. The much Iqwer Incidence
of cancer at these sites in nondrinkers and nonsmokers suggested to these
11-5
researchers that excessive alcohol consumption may augment other process-
es such as impaired nutritional status, which may be associated with the
development of cancer at these sites.
Estimated ethanol intake, independent of smoking, was associated with
a modest, but increased risk for cancers of the upper respiratory tract
(McCoy and Wynder, 1979; Rothman and Keller, 1972). Williams and Horm
(1977) also observed that ethanol increased the risk for cancers at this
site when they controlled for smoking. A number of other reports have
indicated that there is a dose response between consumption of ethanol
(independent of the type of alcoholic beverage) and the risk of upper
respiratory tract cancer (Williams and Horm, 1977; Wynder and Stellman,
1977; Wynder et^ aL. , 1957b). In general, these studies focused on mod-
erate to heavy consumers of ethanol.
Reports by Rothman (1980) and by Burch et_ al^ (1981) indicate that
the risk for cancers of the oral cavity is slightly increased in smokers
reporting low to moderate consumption of ethanol (i.e., >12 to 45 ml, or
approximately 70 to 270 calories daily). However, because consumers tend
to underreport their ethanol intake (DeLuca, 1981), it is difficult to
interpret these findings.
Effect of Nutritional Status
Malnutrition may play a key role in the development of cancers of the
head and neck in alcohol abusers (Kissin and Kaley, 1974). These indi-
viduals frequently suffer from malnutrition because they often consume
from 25% to 50% (or more) of their daily calories as alcohol. In the
absence of chronic alcoholism and smoking, malnutrition or nutritional
imbalance have been found frequently in individuals with cancer of the
oral cavity and respiratory tract (Kissin and Kaley, 1974) . For exam-
ple, an association between Plummer-Vinson (also called Paterson-Kelly)
syndrome and iron deficiency with esophageal cancer has been observed in
Swedish women (Wynder and Fryer, 1958; Wynder and Klein, 1965). Since
the early 1950 f s, dietary supplementation with iron and vitamins has
markedly reduced the incidence of Plummer-Vinson syndrome as well as
esophageal cancer (Larsson et_ l* , 1975). Esophageal cancer in Iran
(Rnet^and Mahboubi, 1972), Sweden (Jacobsson, 1961), and Puerto Rico
(Martinez, 1970) is more frequent among the malnourished. Experi-
mentally induced deficiency of llpotropes, riboflavin, vitamin A, or
zinc have been shown to enhance carcinogen-induced tumors in labora-
tory animals (Newberne and McConnell, 1980).
EXPERIMENTAL EVIDENCE
Po stulat ed Mecfaaiiismfi of Ac t ion -ifr Carcitiogetiesis .:,,-, .
Possibly mechanisms, through which alcohol Might contributes
risk of cancer of the head and neck are: alcohol acting as a carcinogen,
11-6
cocarcinogen, or promoter; alcohol acting as a solvent facilitating
transport of carcinogens across membranes; induction of microsomal
enzymes by alcohol leading to activation and/or metabolism of car-
cinogens; alcohol as a source of putative carcinogenic contaminants
in alcoholic beverages; alcohol-related nutritional deficiencies; and
alcohol abuse associated with immunosuppression. These have been dis-
cussed by Kissin and Kaley (1974), Vitale and Gottlieb (1975), McCoy
and Wynder (1979), Lieber et al. (1979), Schottenfeld (1979), and Vitale
e^al. (1981).
There are only a few experimental data to indicate that alcohol
can act either as a carcinogen or cocarcinogen or that its solvent
properties facilitate the transport of carcinogens across cell mem-
branes. The relationship of alcohol-induced immunosuppression to
tumorigenesis in animals has not been explored, and the role of alco-
hol-related nutritional deficiencies to carcinogenesis in animals is
only in the preliminary stages of investigation.
Alcohol and Induction of Microsomal Enzymes
The chronic feeding of ethanol to laboratory animals can increase
the activity of the hepatic microsomal enzymes responsible for bioacti-
vation of procarcinogens (Rubin e al.. , 1970). Polycyclic hydrocarbons,
e.g., benzo[ajpyrene, were activated to a greater extent when rats were
fed ethanol than when they were fed a control diet (Seitz et:. al . , 1978).
In contrast, Capel ad. (1978) reported a decrease in ben^oJaTjpyrene-
hydroxylase activity following chronic administration of ethanol. McCoy
et_ LL. (1979) demonstrated that ethanol fed to hamsters for 28 days in-
creased the hydroxylation rates of two cyclic nitrosamines, NT-nitroso-
pyrrolidine and N-nitrosonornicotine, which are found in mainstream and
sidestream tobacco smoke. Enhanced mutagenicity of these hydroxylated
compounds was assessed with the Ames test. The enhanced activation of
both nitrosamines by ethanol provides some experimental evidence for the
synergistic effect of chronic alcohol abuse and smoking in the induction
of head and neck cancers. Microsomal activation of tobacco pyrolysate
has been observed in the rat lung, and activation of benzo[a]pyrene
occurs in cultures of small bowel tissue. The metabolic acFivation of
these procarcinogens was increased in tissues chronically exposed to
ethanol by injection (McCoy et_ aJL . , 1979).
Occurrence of Putative Carcinogens in Alcoholic Beverages
Certain congeners of alcoholic beverages, e.g., nitrosamines
(Lijinsky and Epstein, 1970) and fusel oil (Gibel et al., 1968), have
been demonstrated to produce tumors of the stomach~ndTesophagus in
laboratory animals. Other putative carcinogens found in alcoholic
beverages include polycyclic hydrocarbons, such as phenanthrene,
fluoranthrene, benzanthracene, benzo[ajpyrene, and chrysene (Goff and
11-7
Fine, 1979; Masuda et_ al* , 1966), and asbestos fibers, which often leach
from filters into wines (BIgnon t a.1. , 1977; Gaudichet et l . , 1978),
beer (Biles and Emerson, 1968), and gin (Wehman and Plantholt, 1974).
SUMMARY AND CONCLUSIONS
The effects of alcohol consumption on cancer incidence have been
studied in human populations. In some countries, Including the United
States, excessive beer drinking has been associated with an increased
risk of colorectal cancer, especially rectal cancer. This observation
has not been confirmed in most case-control or cohort studies. There
Is limited evidence that excessive alcohol consumption contributes to
hepatic injury and cirrhosis, which in turn may lead to the formation of
hepatomas. Excessive consumption of alcoholic beverages by smokers
appears to act synergistically in increasing the risk for cancer of the
mouth, larynx, esophagus, and the respiratory tract.
11-8
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Med. 3:277-293.
Schwartz, D. 1966. [In French; English Summary.] Alcool et cancer,
fitude de geographic pathologique . Cancro 19:200-209.
11-13
Schwartz, D., J. Lellouch, R. Flamant, and P. F. Denoix. 1962. [In
French; English Summary.] Alcool et cancer. Resultats d'une
equete retrospective. Rev. Fr. Etud. Clin. Biol. 7:590-604.
Schwartz, D., 0. Lasserre, R. Flamant, and J. Lellouch. 1966.
[In French; English Summary.] Alcool et cancer: Stude de
pathologie geographique port ant sur 19 pays. Eur. J. Cancer
2:367-372.
Seitz, H. K., A. J. Garro, and C. S. Lieber. 1978. Effect of chronic
ethanol ingestion on intestinal metabolism and mutagenicity of
benzo(a )pyrene. Biochem. Biophys. Res. Commun. 85:1061-1066.
Sherlock, S., R. A. Fox, S. P. Niazi, and P. J. Scheuer. 1970.
Chronic liver disease and primary liver-cell cancer with
hepatitis-associated (Australia) antigen in serum. Lancet
1:1243-1247.
Spalajkovic, M. 1976. [In French.] Alcoolisme et cancer du larynx
et de l f hypo pharynx. J. Fr. Oto -Rhino-La ryngol. Audio-Phonol.
Chiur. Maxillo-Fac. 25:49-50.
Steiner, P. E. 1956. The etiology and histogenesis of carcinoma
of the esophagus. Cancer 9:436-452.
Stevens, M. H. 1979. Synergistic effect of alcohol on epidermoid
carcinogenesis in the larynx. Otolaryngol. Head Neck Surg.
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Stocks, P. 1957. Cancer Incidence in North Wales and Liverpool
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Cancer Campaign Thirtyfifth Annual Report, Supplement to Part II.
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Multiplicative risks. Bull. Cancer 64:45-60.
X
Tuyns, A. J. , Gi Pequignot , and J. Si Abbatucci. 1979. Oesophageal
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11-14
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11-15
Wynder, E. L. , and S. D. Stellman. 1977* Comparative epidemiology
of tobacco-related cancers. Cancer Res. 37:4608-4622.
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the etiological factors in cancer of the mouth. Cancer
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Swedish study with special reference to Plummer-Vinson
(Pater son-Kelly) syndrome. Cancer 10:470-487.
SECTION B
THE ROLE OF NONNUTRITIVE DIETARY CONSTITUENTS
Section A presented the evidence linking nutrients to carcinogenesis.
In. this* section, which contains Chapters 12 through 15, the committee has
attempted to provide a perspective on the contribution of nonnutritive
dietary components (food additives, contaminants, naturally occurring
carcinogens, and mutagens) to the risk of cancer in humans. The factors
that determined the selection of compounds included in Chapters 12 and 14
and the inherent difficulties in assessing the health effects of food
additives and contaminants are discussed below. Chapter 12 focuses on
naturally occurring substances that are suspected or known carcinogens,
whereas the discussion in. Chapter 13 concentrates on mutagens in foody,
some of which are also carcinogenic. The evidence for carcinogenicity of
food additives and contaminants is reviewed in Chapter 14. The inhiblr-
tory properties of certain nonnutritive synthetic compounds, or-- some ttiat
are present naturally in foods, are presented in Chapter 15.
Technological advances in recent years have led to changes in the
methods of food processing, a greater assortment of food products, and,
a& as result, changes in the consumption patterns of the U.S. popula-
tions The impact of these modifications on human health, especially
the potential adverse effects of food additives and contaminants, has
drawn considerable attention from the news media and the public. Ad-
vances in technology have resulted in an increased use Q Industrial
chemicals, thereby increasing the potential for, cKemifeall contamination
of drinking water and food supplies. The use of processed; foods and,
consequently, of additives has also increased substantially during the
past four decades. Roberts (1981) estimates that more than 55% of the
food consumed In the United States today has been processed to some
degree before distribution to the consumer.
Clearly,, the degree of concern about the health risks from food addi-
tives varies. For example, in ranking the probable sources of health
hazard in the U.S. diet, the Food and Drug Administration (FDA) has con-
sistently listed food additives In fifth or sixth place, well below mi-
crobiological contaminants and witiCirU&t deficiencies. In contrast, con^
sumers surveyed In five cities recneTi<ied that the FDA give high prior-
ity to assessing the safety of food! addltt^es (U.S. Food and Drug Admin-
istration, 1981).
FOOD ADDITIVES
In this report, the term "food additives" is often used generically
to refer to all substances that may be added to foods. However, in the
1958 Food Additives Amendment to the Federal Food, Drug, and Cosmetic
Act, the term has a more restricted legal definition:
B-2
"Food additive" means any substance the intended use of
which results or may reasonably be expected to result,
directly or indirectly, in its becoming a component or
otherwise affecting the character of a food.... (U.S.
Department of Health and Human Services, 1980, p. 4)
The 1958 amendment changed the rules under which food additives were
regulated. Until then, a substance added to food was presumed safe until
someone (usually the government through the FDA) could prove it otherwise;
after 1958, FDA approval of safety was required prior to use. Because
this change in the law would have placed an unmanageable burden on the
manufacturers to conduct the tests required to prove the safety of the
many hundreds of substances then added to foods, the definition of "food
additive" was modified for regulatory purposes to exclude many classes of
substances. The term now covers approximately 400 of the 2,600 to 2,700
substances intentionally added to foods (Code of Federal Regulations,
1981). Not included are approximately 500 food ingredients termed GRAS
(Generally Recognized as Safe) substances; about 100 other "unpublished
GRAS substances; 11 approximately 1,650 flavoring agents, most of which are
classified as GRAS; prior-sanctioned food ingredients, consisting of
about 100 substances approved by the U.S. Department of Agriculture
(USDA) or the FDA prior to 1958; and approximately 30 color additives
(U.S. Department of Health and Human Services, 1980). It would be
difficult to prepare a list of all the compounds in these categories.
Table B-l summarizes the classes of food ingredients covered in the
Federal Food, Drug, and Cosmetic Act and provides examples of each. For
each category, it also presents information concerning the applicability
of the Delaney Clause an amendment to the Act concerning the regulation
of carcinogens. (This amendment and other regulatory actions are
discussed below.)
CONTAMINANTS
Two other, much larger groups of added food constituents are also
included in Table B-l. It is estimated that approximately 12,000
substances are introduced unintentionally during processing, and an
unknown number of other contaminants are inadvertently added to the food
supply. The first group (also called indirect additives) includes by-
products of processing (e.g., caustics used in potato peeling, machinery
cleaners, packaging components), as well as residues of permitted pesti-
cides and of drugs given to animals. There are regulations restricting
the concentrations and types of these compounds in food and the purposes
for which they can be used. Contaminants in the second group, classified
as unavoidable "added" constituents, are regulated when found. For
example, after an accidental contamination by a hazardous chemical, the
concentration of the chemical is compared to established "action levels"
to determine if the foods are fit for human consumption.
B~3
THE DELANEY CLAUSE AND OTHER REGULATORY ACTIONS
The regulation of carcinogens has been a matter of special concern
because it is covered by the Delaney Clause* of the Federal Food, Drug,
and Cosmetic Act. The amendment prohibits the FDA from approving the use
of any food additive found to cause cancer in animals or humans. It has
been criticized as being too restrictive by setting a zero level of risk.
In fact, it applies only to approximately 400 of the 2,700 substances
intentionally added to foods, many of which are GRAS. If any GRAS sub-
stance is found to be carcinogenic, it would no longer be considered GRAS
and would fall under the legal definition of a food additive, thereby
becoming subject to the Delaney Clause.
In addition to the Delaney Clause, numerous amendments to the Federal
Food, Drug, and Cosmetic Act have been made since the early 1960 f s (U.S.
Department of Health and Human Services, 1980). It appears that the stat-
utory provisions governing food safety are a patchwork of divergent, some-
times carefully considered, but sometimes offhand, legislative policies
that invite uneven monitoring of different substances in foods and incon-
sistent treatment of comparable risks from different categories of food
additives.
Recognizing the need to acquire better data and to standardize test-
ing procedures and the criteria for acceptability, the FDA has recently
initiated a review of direct food additives (U.S. Department of Health
and Human Services, 1981). Similarly, the FAO/WHO Joint Expert Committee
on Food Additives acknowledged that the safety of a large number of food
additives remains to be examined or needs to be reevaluated (World Health
Organization, 1980).
Many factors complicate the assessment of nonnutritive dietary
constituents.
Some food constituents are discrete chemical entities that are
easy to test, whereas others are complex, poorly defined mixtures
of natural origin.
Although the Federal Food, Drug, and Cosmetic Act defines various
categories of food ingredients, it is frequently difficult to
determine how to classify certain substances that meet the defini-
tions of more than one category (Code of Federal Regulations,
1981). Information about contaminants is even less precise.
Although most additives and the known contaminants are present
in minute quantities in the diet, little is known about the
chronic effects of low leyels of chemicals on human health, and
even less is known about the potential for synergistic and/or
antagonistic interactions among most of these substances in
foods or in the body.
'Sec. 409(c)(l)(A).
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EXPOSURE OF HUMANS
To determine the risk of carcinogenesis from food additives and
contaminants, it is necessary to know the extent to which humans are
"typically" exposed, the degree of exposure in subgroups of the popu-
lation, the carcinogenic potency of the compound, and the quantity and
quality of the data concerning its toxicity and carcinogenicity.
Although humans are exposed to various additives and contaminants at
levels ranging over several orders of magnitude, some generalizations can
be made about exposure to different classes of substances. The National
Science Foundation (1973) estimated that 0.5% (by weight) of the U.S.
food supply consists of intentional food additives, and the per capita
intake of food additives has increased approximately fourfold in the past
decade. Currently, their use amounts to approximately 5 kg per capita
annually, although as a measure of the average intake of food additives
this may be misleading because approximately one-half of these additives
are used in amounts of 0.5 mg or less (Roberts, 1981). Many intentional
additives are nutritive substances, e.g., sugar, corn syrup, salt, and
dextrose, which are used in large amounts (many kilograms per capita
annually for sugar and corn syrup), whereas many others, e.g., lecithin,
fumaric acid, and sodium bisulfite, are used in quantities that provide
an intake of 10 to 50 g per capita annually. Table B-2 lists the annual
usage of some major classes of food additives (Jorgenson, 1980).
Information about the use of indirect additives by the food industry
is much less precise. Consequently, exposure of humans is difficult to
estimate. It would depend to a large extent on the physical and chemical
characteristics of the additive. For example, packaging materials can
migrate into food. A concentration of 50 Ug/kg in a product consumed at
the rate of 50 g per day would lead to an intake of 2.5 yg of the addi-
tive daily, or <1 mg annually (Roberts, 1981). If the migratory sub-
stances are present in a concentration of 10 mg/kg in a food consumed at
this rate, ^200 mg of additive would be ingested annually (Roberts, 1981).
Most pesticides and industrial chemicals are ingested in trace amounts,
resulting in a daily intake of only a few milligrams or less of each
compound per capita. The daily per capita intake of heavy metals ranges
from 2.4 ug for mercury to 90.2 pg for lead.
The FDA's Market Basket Surveys conducted since the mid-1960 f s have
monitored only a few substances and have excluded convenience foods.
However, they have provided information on the levels of some pesticides,
industrial chemicals, and heavy metals that are ingested as contaminants
in the diet (U.S. Food and Drug Administration, 1980). With a few excep-
tions, information about the exposure to other classes of additives is
estimated indirectly from the amount produced or used in the processing
of foods rather than by direct measurement of actual consumption (National
Academy of Sciences, 1972, 1973, 1978, 1979).
B-7
TABLE B-2
Use of Some Food Additives (Nutritive and Nonnutritive)
in the United States 3
Approximate Quantity
Category (million kg/year)
Thickeners/stabilizers (hydrocollolds) 195 - 215
Flavors and enhancers 132 - 145
Emulsifiers (surfactants) 123 - 136
Acidulants 82 - 91
Chemical leavening agents 80-91
Colors 36 - 39
Humectants 27 " 32
Nutritional supplements (vitamins) 25 - 30
Preservatives 23 - 27
Enzymes > 12
Dietary sweeteners (nonnutrltive) >2.3
Antioxidants 2.3 - 3.6
Sugar b 9,000
Other > 91
a Adapted from Jorgenson, 1980.
b Data from U.S. Department of Agriculture, 1980.
B-8
THE CARCINOGENICITY OF FOOD ADDITIVES AND CONTAMINANTS
Both additives and contaminants have been studied within the United
States and abroad. During the past two decades, these studies have
produced an immense body of literature on the health effects of food
additives. For example, the Select Committee on GRAS Substances (SCOGS)
has published 118 reports on 415 GRAS substances (Fisher and Allison,
1981), and the Flavor and Extracts Manufacturing Association (FEMA) has
compiled approximately 70 reports (Oser and Ford, 1979), which contain
the opinions of an FEMA expert committee on about 1,650 flavoring ingre-
dients used in foods. Since 1958 the FAO/WHO Joint Expert Committee on
Food Additives has prepared annual reports concerning the toxicity of
several hundred additives (World Health Organization, 1958-1980) . The
International Agency for Research on Cancer (1972-1981) has published 24
monographs, many of which evaluate the carcinogenic risk of selected
additives to humans. Before the 1970 1 s, most reports concerned with the
safety of additives were based on data from tests of acute or subchronic
toxicity. These reports documented the general health effects of food
ingredients, but did not necessarily contain comments on carcinogenicity ,
although they did identify substances found to be carcinogenic. More
chronic feeding studies have been conducted during the past decade.
However, the majority of food additives approved for use have not been
tested specifically for carcinogenicity or mutagenicity. Table B-3
summarizes the classes of chemicals tested from 1953 to 1973 in the
National Cancer Institute Carcinogenesis Bioassay Program (National
Cancer Institute, 1975). Very few epidemiological studies have been
conducted to study the effect of food additives. This is probably
because of the difficulty of identifying populations with significantly
different exposures to specific additives, and because of lack of
sensitivity of epidemiological techniques to measure the effects of
exposure to low levels of chemicals.
Eighty-three of the 415 GRAS substances reviewed by SCOGS have been
tested by long-term feeding studies, but very few of these studies were
designed to test for carcinogenicity. A total of 513 GRAS substances
have been tested for mutagenicity and/or by long-term feeding studies.
Because SCOGS was restricted to evaluating each substance only for its
use as a GRAS substance, the determination of safety for many of the
compounds is based on one specific use of the compound. For example,
caffeine was evaluated for its use as an additive in cola beverages only,
not for total exposure from all dietary sources, such as from coffee and
tea (Fisher and Allison, 1981).
Flavoring ingredients have been assessed by FEMA to determine their
safety for specific uses (Oser and Ford, 1979); however, not all ingre-
dients have been tested for mutagenicity and carcinogenicity. Because
several food-coloring agents are suspected or known carcinogens, the
30 or more compounds currently approved for this use in the United
States have been" studied extensively for carcinogenicity. Many pesti-
cides, heavy metals, and industrial chemicals have also been examined
B-9
TABLE B-3
Categories of Compounds Bioassayed for Carcinogenicity
Between 1953 and 1973 a
Percent of Total
Category Bioassayed
Pharmaceuticals 20.8
Pesticides 17.4
Industrial chemicals (organic) 15.2
Metallic compounds 6.7
Natural food products 5.7
Food chemicals 1.6
Tobacco ingredients 0.8
Environmental agents (general) 0.2
Miscellaneous (structural analogues,
multiple uses)
a Data from National Cancer Institute, 1975.
specifically for carcinogenicity and/or mwtagenlcity. Although many
naturally occurring contaminants hav$ al$p been tested for mutagenlcity
and a few for carcinogenicity, much less emphasis has generally been
placed on this class of substances.
Table B-4 lists examples of suspected or proven carcinogens in each
category of food ingredients. With the exception of saccharin, any direct
food additive known to cause cancer in animals or humans has been banned
from use in foods. For kipwn carcinogens in some tlasses of additives,
especially contaminants ol natural origin, the FD^ establishes tolerable
levels. However, for residues of pesticides, the Environmental Protection
Agency establishes limits (Acceptable Daily Intakes) (U.S. Department Of
Health and Human Services, 1980).
B-10
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II
B-12
ASSESSMENT OF EFFECTS ON HUMAN HEALTH
Lack of adequate data on a large number of substances precludes a
comprehensive assessment of the risk to humans exposed to food additives
and contaminants. Therefore, Chapters 12, 13, 14, and 15 contain examples
of nonnutritive substances selected from Table B-4 to illustrate the car-
cinogenic potential of this vast group of substances. The selection of
these examples was determined by the extent to which humans are exposed
through the general diet and the reliability of the data pertaining to
these exposures.
Any assessment of the health effects of food additives and contami-
nants must take into consideration not only the extent to which humans
are exposed through the average diet, but also the wide range of exposure
for subgroups of the population, the wide range in the carcinogenic
potency of these compounds, and the potential for synergistic and/or
antagonistic effects of the numerous compounds that are present in the
average diet.
B-13
REFERENCES
Cater, D. B. 1961. The carcinogenic action of carrageenin in rats.
Br. J. Cancer 15:607-614.
Code of Federal Regulations. 1981. Title 21, Parts 1-99, 100-169,
and 170-199. Office of the Federal Register, National Archives and
Records Service, General Services Administration, Washington, D. C.
Dickens, F., and H. E. H. Jones. 1961. Carcinogenic activity of a
series of reactive lactones and related substances. Br. J. Cancer
15:85-100.
Feron, V. J., C. F. M. Hendriksen, A. J. Speek, H. P. Til, and B. J.
Spit. 1981. Lifespan oral toxicity study of vinyl chloride in
rats. Food Cosmet. Toxicol. 19:317-333.
Fisher, K. D., and R. G. Allison. 1981. Food Additives as Candidates
for Carcinogenicity Testing. Paper prepared for the Committee on
Diet, Nutrition, and Cancer for its meeting of February 17-18,
1981. National Academy of Sciences, Washington, D. C. 36 pp.
[unpublished] .
Gross, M. A., W. I. Jones, E. L. Cook, and C. C. Boone. 1967. Carcino-
genicity of oil of calamus. Proc. Am. Assoc. Cancer Res. 8:24.
Abstract 93.
Hirono, I., H. Mori, M. Haga, M. Fujii, K. Yamada, Y. HIrata,
H. Takanashi, E. Uchida, S. Hosaka, I. Ueno, T. Matsushima, K.
Umezawa, and A. Shlrai. 1979. Edible plants containing carcino-
genic pyrrolizidine alkaloids in Japan. Pp. 79-87 in E. C. Miller,
J. A. Miller, I. Hirono, T. Sugimura, and S. Takayama, eds. Nat-
urally Occurring Carcinogens~Mutagens and Modulators of Carcino-
genesis. Japan Scientific Societies Press, Tokyo; University Park
Press, Baltimore, Md.
Hunter, B., J. Colley, A. E. Street, R. Heywood, D. E. Prentice, and
G. Magnusson. 1978a. Xylitol Tumorigenicity and Toxicity Study in
Long-Term Dietary Administration To Rats -(Final Report). Huntingdon
Research Centre, Htiatingdom, Cambridgeshire , England. Volumes 11-14
of Xylitol* F. Hoffman La Roche Company, Ltd., Basel, Switzerland.
2250 pp.
Hunter, B. , C. Graham, R. Heywood, D. E. Prentice, F. J. C. Rpe, and
D. N. Noakes. 1978b. Tumorigenicity and Carcinogenicity Study with
Xylitol in Long-Term Dietary Administration to Mice (Final Report).
Huntingdon Research Centre, Huntingdon, Cambridgeshire, England.
Volumes 20-23 of Xylitol. F. Hoffman La Roche Company , Ltd ., Basel,
Switzerland. 1500pp.
B-14
International Agency for Research on Cancer. 1973. IARC Monographs
on the Evaluation of the Carcinogenic Risk of Chemicals to Man.
Volume 3. Certain Polycycllc Aromatic Hydrocarbons and Heterocyclic
Compounds. International Agency for Research on Cancer, Lyon,
France. 271 pp.
International Agency for Research on Cancer. 1974a. IARC Monographs on
the Evaluation of the Carcinogenic Risk of Chemicals to Man. Volume
5. Some Organochlorine Pesticides. International Agency for Re-
search on Cancer, Lyon, France. 241 pp.
International Agency for Research on Cancer. 1974b. IARC Monographs
on the Evaluation of the Carcinogenic Risk of Chemicals to Man.
Volume 7. Some Anti-Thyroid and Related Substances, Nitrofurans and
Industrial Chemicals. International Agency for Research on Cancer,
Lyon, France. 326 pp.
International Agency for Research on Cancer. 1975. IARC Monographs
on the Evaluation of the Carcinogenic Risk of Chemicals to Man.
Volume 8. Some Aromatic Azo Compounds. International Agency for
Research on Cancer, Lyon, France. 357 pp.
International Agency for Research on Cancer. 1976a. IARC Monographs
on the Evaluation of the Carcinogenic Risk of Chemicals to Man.
Volume 10. Some Naturally Occurring Substances. International
Agency for Research on Cancer, Lyon, France. 353 pp.
International Agency for Research on Cancer. 1976b. IARC Monographs
on the Evaluation of the Carcinogenic Risk of Chemicals to Man.
Volume 12. Some Carbamates, Thiocarbamates and Carbazldes.
International Agency for Research on Cancer, Lyon, France. 282 pp.
International Agency for Research on Cancer. 1977. IARC Monographs
on the Evaluation of the Carcinogenic Risk of Chemicals to Man.
Volume 13. Some Miscellaneous Pharmaceutical Substances.
International Agency for Research on Cancer, Lyon, France. 255 pp.
International Agency for Research on Cancer. 1978a. IARC Monographs
on the Evaluation of the Carcinogenic Risk of Chemicals to Man.
Volume 16. Some Aromatic Amines and Related Nitro Compounds Hair
Dyes, Colouring Agents and Miscellaneous Industrial Chemicals.
International Agency for Research on Cancer, Lyon, France. 400 pp.
International Agency for Research on Cancer. 1978b. IARC Monographs on
the Evaluation of the Carcinogenic Risk of Chemicals to Humans.
Volume 18. Polychlorinated Biphenyls and Polybrominated Biphenyls.
International Agency for Research on Cancer, Lyon, France. 140 pp.
International Agency for Research on Cancer. 1979a. IARC Monographs
on the Evaluation of Carcinogenic Risk of Chemicals to Humans.
Volume 20. Some Halogenated Hydrocarbons. International Agency for
Research on Cancer, Lyon, France. 609 pp.
B-15
International Agency For Research on Cancer. 1979b. IARC Monographs
on the Evaluation of the Carcinogenic Risk of Chemicals to Humans.
Volume 21, Sex Hormones (II). International Agency for Research on
Cancer, Lyon, France. 583 pp.
International Agency for Research on Cancer. 1980. IARC Monographs on
the Evaluation of the Carcinogenic Risk of Chemicals to Humans.
Volume 22, Some Non-Nutritive Sweetening Agents. International
Agency for Research on Cancer, Lyon, France. 208 pp.
Jorgensen, D. J. 1980. The need of additives in industry. Pp. 652-677
in H. D. Graham, ed. The Safety of Foods. Second edition. AVI
Publishing Company, Westport, Conn.
Kraybill, H. F. 1976. Food chemicals and food additives. Pp. 245-318
in P. M. Newberne, ed. Trace Substances and Health: A Handbook.
Part 1. Marcel Dekker, New York and Basel.
Merrill, R. A. 1978. Regulating carcinogens in food: A legislator's
guide to the food safety provisions of the Federal Food, Drug, and
Cosmetic Act. Mich. Law Rev. 77:171-250.
National Academy of Sciences. 1972. A Comprehensive Survey of Industry
on the Use of Food Chemicals Generally Recognized as Safe (GRAS)
(Comprehensive GRAS Survey). A report prepared by the Subcommittee
on Review of GRAS List Phase II. National Academy of Sciences,
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National Academy of Sciences. 1973. The tyse of Chemicals in Food
Production, Processing, Storage, and Distribution. A report
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Board. National Academy of Sciences, Washington, D.C. 34 pp.
National Academy of Sciences. 1978. 1975 Re survey of the Annual
Poundage of Food Chemicals Generally Recognized as Safe (GRAS).
Committee on GRAS List Survey Phase III. National Academy of
Sciences, Washington, D.C. 23 pp.
National Academy of Sciences. 1979. The 1977 Survey of Industry on
the Use of Food Additives. Volume 1, Description of the Survey;
Volume 2, Summarized Data; Volume 3, Estimates of Daily Intake.
Food and Nutrition Board, National Academy of Sciences, Washington,
D.C. 2,135 pp. Available from the National Technical Information
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National Academy of Sciences. 1981. The Health Effects of Nitrate,
Nitrite, and N-Nitroso Compounds. Part 1 of a 2-Part Study by the
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National Academy Press, Washington, D.C. 544 pp.
B-16
National Cancer Institute. 1975. Survey of Compounds Which Have Been
Tested for Carcinogenic Activity. 1972-1973 Volume. National
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Possible Carcinogenicity. NCI Carcinogenesis Technical Report
Series No. 157. DHEW Publication No. (NIH) 79-1713. Carcinogenesis
Testing Program, National Cancer Institute, Bethesda, Md. 112 pp.
National Science Foundation. 1973. Chemicals and Health. Report
of the Panel on Chemicals and Health of the President's Science
Advisory Committee, September 1973. Science and Technology Policy
Office, National Science Foundation, Washington, B.C. 211 pp.
Norris, J. M. 1977. Status Report on the 2 Year Study Incorporating
Acrylonitrile in the Drinking Water of Rats. Health and Environ-
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(unpublished) .
Oser, B. L., and R. A. Ford. 1979. Recent progress in the considera-
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12. GRAS substances. Food Technol. 33(7): 65-73.
Roberts, H. R. 1981. Food safety in perspective. Pp. 1-13 in H. R.
Roberts, ed. Food Safety. John Wiley & Sons, New York.
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Food and Drug Administration, U.S. Department of Health and Human
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Principles and Procedures for Direct Food Additive Cyclic Review
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B-17
U.S. Food and Drug Administration. 1981. Consumers participate in FDA's
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Additives. WHO Tech. Rep. Ser. 648:1-45.
CHAPTER 12
NATURALLY OCCURRING CARCINOGENS
The production of toxic compounds by living cells has long been
recognized. Some of these chemicals, especially those produced by
microbes and plant cells, have carcinogenic activity. Although some
of these compounds are integral components of foods that are relatively
common in the diet of humans, many of them have been found either in
unusual food sources or in foods contaminated by microorganisms or
unwanted plant materials. The potential hazards to human health posed
by these components or contaminants of foods range from slight to very
great. For example, very low levels of exposure to chemicals with
relatively weak carcinogenic activity in laboratory animals may pose
little risk to human populations. On the other hand, the presence of
aflatoxin B^ in foods is a matter of great concern, since aflatoxin
BI is a potent carcinogen for a number of species and epidemiological
data suggest that this carcinogen may play a role in the development of
cancer in humans living in some parts of Africa and in the Far East
(Peers je a.1. , 1976; van Rensburg t al. , 1974).
Much of the literature on the carcinogenic products of living cells
has been collected and evaluated by working groups of the International
Agency for Research on Cancer (1976) and by the National Research Coun-
cil (National Academy of Sciences, 1973). Accordingly, these compre-
hensive reviews are often cited in this chapter instead of the primary
literature. In addition, several recent reviews on naturally occurring
carcinogens include exhaustive lists of primary references pertaining
to these carcinogens. The overviews also cite literature on certain
aspects of these carcinogens not covered in this chapter, such as their
metabolic activation and deactivation, the reactions of electrophilic
derivatives with cellular macromolecules, and the biochemical and
biological consequences of the latter reactions (Hirono, 1981; Miller
and Miller, 1979; Miller et al., 1979; Schoental, 1976).
MYCQTQXINS
By definition, mycotoxins are toxic secondary products resulting
from the metabolism of molds. In this chapter, the committee has
reviewed only those toxic metabolites of mold that occur as natural
contaminants of food or feed or that demonstrate some evidence of car-
cinogenicity in mammals when administered orally. Although at least
45 mycotoxins have been identified as eliciting some type of carcino-
genic or mutagemic response, only 17 of them have been reported to
occur naturally in food or feed (Stoloff > in press) (or only 13, if
the aflatoxin group is considered as a single compound)
12-2
The selection of the mycotoxins discussed in this section was
based on the extent of their occurrence in food and/or the data demon-
strating their carcinogenicity. These compounds include: aflatoxins,
sterigmatocystin, ochratoxin A, zearalenone, T-2 toxin, patulin, pen-
icillic acid, griseofulvin, luteoskyrin, cyclochlorotine, and ergot.
Aflatoxins
A very extensive effort has gone into the study of this group of
mycotoxins, especially to examine its most potent member, aflatoxin
BI Much more is known about the occurrence and toxicity of the
aflatoxins than about any other myco toxin and, probably, most other
natural contaminants.
The scattered data pertaining to worldwide occurrence of aflatoxins
in food were compiled for a conference on mycotoxins, which was spon-
sored by the Food and Agriculture Organization, the United Nations
Environment Program, and the World Health Organization (1977). More
recently, Stoloff (in press) compiled data on the occurrence of afla-
toxins in the United States.
The af latoxin-producing molds Aspergillus flavus and A. parasiti-
cus are ubiquitous. They are frequently encountered as outgrowths on
stored commodities under conditions prevailing in many tropical areas.
In the United States, aflatoxin contamination is generally restricted
to those crops invaded by the af latoxin-producing molds before harvest:
most frequently peanuts, corn, and cottonseed, and to a much lesser
extent tree nuts, including almonds, walnuts, pecans, and pistachios.
The extent of contamination is greater in the southeastern United
States.
In the United States, humans are exposed to aflatoxin mostly from
corn and peanuts (U.S. Food and Drug Administration, 1979). Other
direct dietary sources, such as tree nuts, are of minor significance,
either because contamination is infrequent or because only small
quantities are consumed.
It is unlikely that secondary exposures result from the ingestion
of aflatoxin residues in tissues of animals fed aflatoxin-contaminated
feed (Stoloff, 1979), except for aflatoxin M X , a metabolite that
appears in the milk of lactating mammals exposed to aflatoxins. But,
although large amounts of milk are consumed, this exposure is negligi-
ble compared to the direct exposure from peanuts and corn,
Aflatoxins are classified as unavoidable contaminants. In the
United States, the maximum allowable limit of total aflatoxins in
consumer peanut products is currently 20 pg/kg (U.S. Food < aod "" Bttug
Administration, 1980b).
12-3
Epidemiological Evidence* Oettle (1965) was the first investi-
gator to draw serious attention to the hypothesis that aflatoxin
ingestion might cause liver cancer. He suggested that the geographic
distribution of liver cancer in Africa could be explained by differing
levels of exposure to aflatoxin in the diet. Keen and Martin (1971)
reported an apparent association between the consumption of groundnuts
contaminated with aflatoxin and the occurrence of liver cancer in
different areas of Swaziland. Alpert et^ al^. (1971) made a similar
correlation of contaminated foodstuffs and incidence of hepatoma by
tribe and by province or district in Uganda. In a later study in
Swaziland, Peers ej^ aJU (1976) analyzed aflatoxin levels in foods
consumed by a representative sample of the population in 11 geographic
areas. He reported a significant correlation between aflatoxin contam-
ination and incidence of primary liver cancer among adult males. A
similar study in the Murang'a district of Kenya (Peers and Linsell,
1973) indicated that there was a correlation between aflatoxin levels
in dietary staples of three district subdivisions and the incidence of
liver cancer. Mozambique has particularly high rates of liver cancer,
perhaps the highest in the world, and studies of aflatoxin contamina-
tion of foods indicated that the estimated daily intake of aflatoxin in
that country was higher than that reported for any other country (van
Rensburg et^ al^ 1974). One problem recognized by the researchers in
all of these studies is the inadequacy of the data on liver cancer
incidence, since cancer registration is not well established in these
areas.
Detailed studies of aflatoxin contamination of ingested foodstuffs
have also been conducted in Thailand, where there was an overall corre-
lation between estimated aflatoxin intakes in two regions and liver
cancer incidence (Shank eal., 1972a,b; Wogan, 1975). The frequency
with which aflatoxin was detected in foods has also been correlated
with liver cancer mortality in Guangxi province in China (Armstrong,
1980). In Taiwan, where liver cancer mortality rates are high, Tung
and Ling (1968) reported that dietary staples (e.g., peanuts and peanut
oil, which is widely used in cooking) are frequently contaminated with
aflatoxin.
Linsell and Peers (1977) observed a strong correlation between
estimated levels of aflatoxin ingested and liver cancer incidence from
various studies conducted in Africa and Asia. They further noted that
there were no areas where high levels of aflatoxin ingestion have been
associated with low rates of liver cancer.
Although the studies described above suggest that aflatoxin causes
primary hepatocellular carcinoma (PHC), numerous other reports have
also documented a high correlation between PHC and exposure to hepati-
tis B virus (Chien et al., 1981; Prince et al., 1975; Simons et, al,
1972; Tong t al . , 17717 Vogel e al . , ITTQJ7 These studies cto" not
indicate whether present or past exposure to this virus is more closely
associated with the development of PHC. However, Kew et_ al . (1979)
12-4
reported that active hepatitis B viral infection is present in approxi-
mately 80% to 90% of the patients with PHC. Approximately 5% to 10% of
the victims of hepatitis B infection actually develop chronic active
hepatitis with persistent liver damage. The liver cells of these indi-
viduals are believed to regenerate more rapidly, thereby increasing the
likelihood that a biochemical lesion that initiates neoplasia will
become fixed in the genes of the subsequent cell population.
The worldwide occurrence of hepatitis B viral infection is similar
to that of primary hepatocellular carcinoma. However, it is possible
that the influences of aflatoxin and hepatitis B virus on the risk for
PHC are not completely independent. Van Rensburg (1977) reviewed the
evidence for both risk factors and concluded that preexisting viral in-
fection is probably a prerequisite for malignant transformation by afla-
toxin.
The possibility that aflatoxin may also be involved in the etiology
of esophageal cancer is suggested by the correlation between mortality
from esophageal cancer and the consumption of large amounts of pickled
vegetables and other fermented or moldy food in Linxian county of Henan
province in northern China (Yang, 1980). Although Aspergillus flavus
has been isolated from some products, it is difficult to determine the
role of aflatoxin in the etiology of this disease because these foods
also contain other fungal species, mutagens, and carcinogens, including
N nitroso compounds.
Epidemiological studies have not been undertaken in Western coun-
tries, but there have been reports indicating the presence of aflatoxin
B-^ in autopsy samples from liver cancer patients in Czechoslovakia
(Dvorakova et_ ail. , 1977), New Zealand (Becroft and Webster, 1972), and
the United States (Siraj et_ al. , 1981). Siraj <et al. (1981) detected
aflatoxin Bj_ in four of the six liver samples obtained from patients
with PHC in the United States. The significance of these findings is
not yet known.
Experimental Evidence: Carcinogenicity. Aflatoxin Bj is the
most potent hepatocarcinogen known, being about 1,000 times more
powerful than butter yellow (-dimethylaminoazobenzene) in rats. The
carcinogenicity of aflatoxins has been examined in several studies in a
variety of species and strains of laboratory animals, including mice,
marmosets, tree shrews, trout, ducks, rhesus monkeys, hamsters, and
several strains of rats (Wogan, 1973). Of the various species tested,
the male Fischer 344 rat was the most sensitive to aflatoxin-induced
carcinogenesis (Wogan, 1973).
Aflatoxin Bj induced mainly hepatocellular carcinomas in rats.
However, other studies in rats have indicated that it may also induce a
very low incidence of carcinomas of the glandular stomach (Butler and
Barnes, 1966), cancers of the colon (Newberne and Rogers, 1973; Wogan
and Newberne, 1967), renal epithelial neoplasia (Epstein et 1., 1969),
12-5
and lung adenomas (Newberne et^ aJ^ , 1967). Within a susceptible
species and strain, males are much more susceptible than females to
challenge with aflatoxin (Wogan and Newberne, 1967).
Mice are resistant to aflatoxin-induced carcinogenesis under con-
ditions that result in 100% tumor incidence in Fischer rats. However,
hepatomas were induced in 82 of 105 inbred (C57BL X C3H)F;L mice in-
jected intraperitoneally during the first 7 days after birth with doses
of aflatoxin B^ as low as 1.25 pg/g body weight (bw) and killed 82
weeks later (Vesselinovitch e al. , 1972).
In comparison to Fischer rats, nonhuman primates (170 animals in 12
different investigations) were relatively resistant to aflatoxin-induced
carcinogenesis (Stoloff and Friedman, 1976). Liver tumors do not occur
spontaneously in monkeys (O'Gara and Adamson, 1972), but a female rhesus
monkey developed a primary liver carcinoma after ingesting approximately
500 mg of aflatoxin B^ over a 6-year period (Adamson e al,. , 1973). In
another study, one of nine marmosets developed liver tumors after 50 weeks
on a diet (5 days a week) containing aflatoxin B^ at 2 pg/g (Lin et al . ,
1974). However, the authors also observed liver cirrhosis, which is not a
symptom of af latoxicosis in rats. Reddy et_ al, (1976) reported that 9 of
18 tree shrews intermittently fed aflatoxin B^ at 2 pg/g diet developed
liver cancers after 74 to 172 weeks of treatment.
Experimental Evidence: Mutagenicity. Aflatoxin B-^ was shown to be
mutagenic to Salmonella typhimurium strains TA98 and TA100 with and with-
out S9 fraction (Ueno et_ al . , 1978). It was positive in the Bacillus
subtilis rec assay (Ueno and Kubota, 1976). In FM3A mouse cells, afla-
toxin induced 8-azaguanine-resistant mutants as well as chromosome aber-
rations (Umeda e al . , 1977). Aflatoxin M^, the metabolite of aflatoxin
B lf was mutagenic in the Ames test (Wong and Hsieh, 1976), but inactive
in B. subtilis rec assay (Ueno and Kubota, 1976).
Other My co toxins
Table 12-1 summarizes the data on the occurrence, carcinogenicity,
and mutagenicity of mycotoxins other than aflatoxins that may be found
in food. Although most of these mycotoxins are mutagenic in bacterial
systems and other short-term tests and/or are carcinogenic in laboratory
animals, there are no epidemiological studies pertaining to their role
in neoplasia in humans.
Summary and Conclusions; Aflatoxins and Other Mycotoxins
A consistent body of evidence, all based on correlational data,
associates the contamination of foods by aflatoxia with a high incidence
of liver cancer in parts of Africa and Asia, but there is no epidemiologi-
evidence that aflatoxin contamination of foodstuffs is related to
12-6
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12-7
cancer risk In the United States. Epidemiological studies have also
indicated a high correlation between primary hepatocellular carcinoma
and exposure to hepatitis B viral infection. Aflatoxin is carcinogenic
in several species of animals, including rats, mice, trout, ducks,
monkeys, and marmosets, and there is evidence of dose response. It
induces mainly tumors of the liver and, to a lesser extent, tumors In
the kidney, lung, stomach, and colon, more readily in males and in the
young. The carcinogenicity of aflatoxin is paralleled by its
mutagenicity in various systems.
There is no reliable information about the role of other mycotoxins
in carcinogenesis in humans.
HYDMZINES IN MUSHROOMS
Epidemiological Evidence. No epidemiological studies have been
conducted to determine the effects of hydrazines on carcinogenesis in
humans .
Agaricus bisporus
Agaricus bisporus is a commonly eaten cultivated mushroom in
Europe, North America, and other parts of the world. The exact
consumption figures for Agaricus blgporus are unknown, but the U.S.
Department of Agriculture (1981) has estimated that approximately 213
million kilograms of this mushroom were available for consumption
(production and imports) in the United States during 1980.
Agaricus bisporus contains agaritine $-N-[Y-L(+)~glutamyl]~4~
hydroxymethylphetiylhydrazine (Toth eal. , 1978) and 4-(hydroxy-
methyl)benzenediazonium ion (Levenberg, 1962). 4- Hydroxymethylphenyl-
hydrazine and 4-methylphenylhydrazlne, which are breakdown products of
agaritine, have also been found in A. bisporus (Levenberg, 1964).
Experimental Evidence: Carcinogenicity. II 1 ~Acetyl~4~(hydroxy~
methyl)phenylhydrazine as a 0.0625% solution in drinking water admin-
istered continuously to Swiss mice from 6 weeks of age to the end of
their lives Induced lung and blood vessel tumors (Toth et^ al . , 1978).
4-(Hydroxyiaethyl)benzenedIazqnluii tetrafluoroborate administered
to Swiss mice it t weekly subcutaneous injections at 50 yg/g bw
resulted in an increased incidence of tumors of the subcutis and skin
(Toth e a]L., 1981).
4-Methylphenylhydrazine hydrochloride administered to Swiss mice In
7 weekly intragastric instillations of 250 yg/g bw Induced lung and
blood vessel tumors (Toth et al., 1977).
12-8
Experimental Evidence; Mutagenicity. N ' -Acetyl-4- ( hydroxy-
methyl)phenylhydrazine was most mutagenic in S^. typhimurium TA1537
without metabolic activation, and it exhibited marginal DNA-modifying
activity only when the S9 fraction was included (Rogan ! in
press) .
4~(Hydroxymethyl)benzenediazonium tetrafluoroborate was weakly
mutagenic in TA1535 and strongly mutagenic in TA1537, exhibiting tox-
icity in both strains (Rogan e .1. , in press).
Agaritine produced equivocal results in both in vitro assays. There
was a slight enhancement of mutagenicity in . typhimurium TA1537 with-
out metabolic activation, and marginal DNA-modifying activity in the
presence of S9 fraction (Rogan et al. , in press).
4-Methylphenylhydrazine hydrochloride was also found to be mutagenic
with and without S9 fraction in S_. typhimurium TA98 and TA100 (Shimizu
et al., 1978).
Gyromitra esculenta
Each year, approximately 1 million people throughout the world eat
the mushroom Gyromitra esculenta (Simons, 1971); 100,000 of these
people reside in the United States (S. Miller, personal communication).
The literature contains more than 500 reports of poisonings resulting
from the ingestion of this mushroom. Some of these incidents were
fatal (Franke et_ a.1. , 1967).
Experimental Evidence: Carcinogenicity. Eleven hydrazines and
hydrazones have been identified in . esculenta* Studies have been
conducted to determine the carcinogenicity of many of these compounds.
Continuous administration of 0.0078% NHnethyl-N-f ormylhydrazine
(MFH) in drinking water to 6-week-old outbred Swiss mice for life pro-
duced tumors of the liver, lung, gallbladder, and bile duct. A higher
dose (0.0156% MFH) given under identical conditions had no tumorigenic
effect, since it proved too toxic for the animals (Toth and Nagel,
1978). Subsequently, the carcinogenicity of MFH was confirmed in mite
(Toth and Patil, 1980, 1981) and in Syrian hamsters (Toth and Patil,
1979).
Acet aldehyde methylformylhydrazone, the main ingredient of jG. escu-
lenta, was administered to Swiss mice in propylene glycol in 52 weekly
intragastric instillations at 100 pg/g bw (Toth e al. , 1981). The
treatment induced tumors of the lungs, preputial glands, forestomach,
and clitoral glands.
Drinking water solutions of 0.001% hydrazine, Q.01% methylhydrazine,
and 0.001% methylhydrazine sulfate were administered continuously to 5-
and 6-week-old randomly bred Swiss mice for their lifetimes. Hydrazine
12-9
and methylhydrazine sulfate significantly increased the incidence of
lung tumors in Swiss mice, whereas methylhydrazine enhanced the
development of this neoplasm by shortening its latent period (Toth,
1972).
A 0.01% solution of methylhydrazine was administered daily in the
drinking water of 6-week-old randomly bred Syrian golden hamsters for
the remainder of their lifetimes. The treatment produced malignant
histiocytomas of the liver and tumors of the cecum (Toth and Shimizu
1973).
Experimental Evidence: Mutagenicity. N-Methyl-N-formylhydrazine,
which is present in esculenta, was mutagenic only in ^. typhimurium
TA1537 without activation and had no DNA-modifying activity (Rogan et
al. , in press).
Methylhydrazine was mutagenic in S^. typhimurium TA1535 and TA1537.
The addition of S9 fraction activating^ system enhanced the mutagenicity
in both strains (Rogan et ad. , in press). The DNA-modifying activity
was observed earlier by von Wright et al. (1977).
Summary and Conclusions ; Hydrazines
Studies have shown that some chemical constituents of the Agaricus
bisporus mushroom are carcinogenic in mice and mutagenic in bacterial
systems. One constituent has also been shown to be carcinogenic in ham-
sters. But the findings of these studies are not sufficient for conclu-
sions to be drawn concerning the risk to humans.
Some derivatives of hydrazines in the fungus Gyromitra esculent a
have proven carcinogenic in a number of organs and tissues of mice and
hamsters. Two of them were mutagenic in bacterial systems. There are
no epidemiological studies concerning the carcinogenicity of these
mushrooms in humans.
PLANT CONSTITUENTS AND METABOLITES
Pyrrolizidine Alkaloids
Pyrrolizidine alkaloids occur in many nonedible plant species,
including the genera Senecio (ragworts), Crotalaria (rattleboxes), and
Heliotropium (heliotropes), in amounts ranging from trace amounts to as
much as 5% of the dry weight. In general, members of this group that
contain a nuclear double bond alpha to an esterified carbinol are very
potent toxins in the liver and lung of rodents and certain farm live-
stock (Hirono, 1981; Hirono t a^l. , 1979; International Agency for
Research on Cancer, 1976).
Experimental Evidence; Carcinogenicity. Monocrotaline, retrorsine,
lasiocarpine, heliotrine, senkirkine, symphytine, and petasitenine, all
12-10
of which are a, g-unsaturated esters , are carcinogenic when administered
to rats orally or parenterally under conditions that permit long-term
survivals. Most frequently, tumor induction has involved multiple doses
of the alkaloids at moderate levels (e.g., a 0.01% solution of petasite-
nine in drinking water for 480 days) (Hirono et_ aJU , 1979), but low in-
cidences of tumors after long latent periods have apparently resulted
from only one or a few doses. Tumors have also been induced in rats
after the administration of plants, such as coltsfoot (Tussilago far-
fara) or comfrey (Symphytum sp.)> which contain high levels of pyrrol-
izidine alkaloids. The tumors occur most frequently in the liver, but
some have developed in other tissues, including the skin and lungs.
Plants containing the pyrrolizidine alkaloids may contaminate
forages and food grains. Such contamination has resulted In acute and
chronic poisoning of livestock in some parts of the world (Schoental,
1976). Humans may also be exposed by consuming such alkaloid-containing
plants as drugs or foods. For example, one species of comfrey (Sym-
phytum officinale) is consumed as a green vegetable in Japan (Hirono et_
al., 1979). The carcinogenic potency of some pyrrolizidine alkaloids
and their widespread occurrence have led to the suggestion that these
a, 6-unsaturated esters may play a role in the induction of hepatic
cancer in humans in some parts of the world; however, there are no
reliable data to support this hypothesis.
Experimental Evidence: Mutagenlcity. Retrorsine, lasiocarpine,
hello trine, senkirkine, symphytine, and petasitenine, but not monocrota-
line, have been shown to be mutagenic in the Salmonella/ml crosome assay
(Hirono et al., 1979; Wehner et al., 1979; Yamanaka et al., 1979).
Allylic and Propenylic Benzene Derivatives
Numerous allylic and propenylic benzene derivatives are present In
the essential oils of a wide variety of plants (Guenther, 1948-1952;
Guenther and Althausen, 1949), and some of these plants or their ex-
tracts are used as flavoring agents for human foods or as medicines
consumed by humans. Of the known naturally occurring allylic benzene
derivatives, safrole (l-allyl-3,4-methylenedioxybenzene), which is a
major component of oil of sassafras, and estragole (l-allyl-4-methoxy-
benzene), which is present in tarragon and anise, have been the most
comprehensively studied.
Experimental Evidence; Carcinogenicity. Safrole has induced low-
to-moderate incidences of hepatic tumors in adult rats fed at levels of
0.5% or more of the diet for as long as 2 years (International Agency
for Research on Cancer, 1976). Both safrole and estragole induced
hepatic tumors and subcutaneous angiosarcomas within 18 months after
they were fed to adult female CD-I mice at levels tif 0. 25%-0. 5% for ap-
proximately 1 year (Miller et al., 1979). Administration of ls^ than
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1 mg of either compound or of methyl eugenol to CD-I or (C57BL/6 x
C3H/He)Fi male mice prior to weaning resulted in a high incidence of
hepatomas by the age of 12 months (Miller et_ al. , 1979).
Experimental Evidence: Mutagenicity* Saf role was mutagenic in
vitro and in the host-mediated assay (Green and Savage, 1978). However,
McCann t al, (1975), Swanson et_ al. (1979), and Wislocki et^ al. (1977)
reported that it was not mutagenic in the Ames test. It was positive
in Bacillus subtilis rec assay (Rosenkranz and Poirier, 1979) and in
Saccharomyces cerevisiae D3 (Simmon, 1979).
Estragole was mutagenic to S^ typhimurium TA100 (Swanson et al . ,
1979). Eugenol was not mutagenic to Ames Salmonella strains in vitro
and in the host-mediated assay (Green and Savage, 1978; Swanson et al. ,
1979).
Bracken Fern Toxin(s)
Bracken fern (Pteridium aquilinum) occurs widely in nature and is
consumed by humans in several parts of the world, especially in Japan
(Hirono, 1981). For at least 30 years, it has been known that consump-
tion of this plant causes damage to the bone marrow and intestinal
mucosa of cattle, but the precise compound(s) responsible for these
toxic effects have not been identified.
Epidemiological Evidence; Carcinogenic! ty. In a prospective cohort
study in Japan, Hirayama (1979) found a significantly higher risk of
esophageal carcinoma associated with the daily intake of hot gruel or
bracken fern every day, especially in people who ate both foods daily.
However, Howe ejt al. (1980) found no association between bladder cancer
and consumption oTlfiddlehead greens (related to bracken fern) in a
case-control study in Canada.
Experimental Evidence: Carcinogenicity. The carcinogenicity of
bracken fern was first suspected by Pamukcu in 1960, who found polyps
in the urinary bladder mucosa of cattle fed large amounts of bracken
fern for long periods (Pamukcu and Bryan, 1979). Since that time,
ingestion of high levels of bracken fern (25% to 40% of the diet) has
been found to result in the formation of urinary bladder carcinomas in
cattle, urinary bladder carcinomas and intestinal adenocarcinomas in
rats, urinary bladder tumors in guinea pigs, pulmonary adenomas in
mice, and intestinal adenocarcinomas in Japanese quail (Evans, 1976).
Hirono (1981) reported that the greatest concentration of the
toxin(s) is present in young plants before the fronds have uncurled,
and the carcinogenic activity of the rhizome is greater than that of
the stalk or fronds. The toxicity of tbe fetrji is reduced & but not
eliminated, by cooking.
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A number of studies have been conducted to identify the carcinogenic
agent(s) in bracken fern (Evans, 1976; Hirono, 1981; Pamukcu and Bryan,
1979). Quercetin (3,3 f ,4 f , 5, 7-pentahydroxyflavone) occurs as a conju-
gate in bracken fern and in numerous other plants. In culture, this
compound has induced morphological transformation of cryopreserved
golden hamster embryo cells (Umezawa et al. , 1977) and mutations in J[.
typhimurium (Bartholomew and Ryan, 1980), but its carcinogenicity in
rats continues to be disputed. In one study, administration of 0.1%
quercetin in the diet of rats for as long as 1 year resulted in an 80%
incidence of intestinal tumors and a 20% incidence of urinary bladder
tumors (Pamukcu et_ aJU , 1980). However, in another laboratory, adminis-
tration of quercetin as 1% or 5% of the diet for 540 days or as 10% of
the diet for 850 days did not result in a significant incidence of
tumors in ACI rats (Hirono e al . , 1981).
Interest in the possibility that bracken fern might play a role in
the induction of cancers stems from the knowledge that it is used by
humans as food in several parts of the world (Hirono, 1981). Indirect
evidence for its carcinogenicity is derived from observations that milk
from cows fed high levels of bracken fern contained compounds that were
shown to be carcinogenic in rats. Carcinomas of the intestine, urinary
bladder, and kidney pelvis were observed in rats fed high levels of
fresh or powdered milk from cows that had consumed 1 g of bracken fern
per kilogram of body weight daily for approximately 2 years, but not in
rats fed milk from control cows (Pamukcu et al., 1978).
Estrogenic Compounds
The plant estrogens include estrone (from palm kernels), genistein
(from soybean and clover), coumestrol (from alfalfa and other forage
crops), and mirestrol (from certain legumes) (Schoental, 1976; Stob,
1973). Zearalenone, a product of Fusarium molds that sometimes infect
grains, also possesses estrogenic activity.
Plant estrogens are very weak estrogens compared to the hormones
from animals; however, they can occur in relatively large amounts. For
example, fat-free soybeans may contain as much as 0.1% of genistein
(Verdeal et_ al^. , 1980) .
Experimental Evidence; Carcinogenicity. Other than one report on
zearalenone (discussed earlier in this chapter), there are no data
pertaining to the carcinogenicity of plant estrogens. Some nonsteroidal
phytoestrogens that are natural components of some foods compete for es-
trogen receptors in rat uterine cytosol in tissue sections from 7,12-
dime thy Ibenz [aj anthracene-induced mammary tumors, and in mammary tumor
tissue from humans (Verdeal e al. , 1980) . The significance of these
findings in the etiology of neoplasia in humans is not known.
12-13
Experimental Evidence: Mutagenicity . Genistein and coumestrol
were not mutagenic in the Salmonella microsome assay (Bartholomew and
Ryan, 1980).
Coffee
Epidemiological Evidence: Carcinogenicity; Coffee drinking has
been associated with elevated risk for bladder cancer in several case-
control studies (Bross and Tidings, 1973; Cole, 1971; Fraumeni e t al . ,
1971; Howe e al . , 1980; Miller t al . , 1978; Simon et al. , 1975;
Wynder and Goldsmith, 1977). However, with only two possible excep-
tions in males (Bross and Tidings, 1973; Wynder and Goldsmith, 1977),
there has been no evidence of a dose-response relationship, and it
appears that the association is not causal.
A direct association of coffee consumption with risk of pancreatic
cancer based on case-control data was reported by MacMahon et al.
(1981). They provided evidence for a dose-response relationship. In
another report, Lin and Kessler (1981) noted an association between pan-
creatic cancer and the use of decaffeinated coffee specifically. In an
earlier geographical correlation of per capita food intake and mortality
from cancer, Stocks (1970) observed a significant association between
coffee drinking and pancreatic cancer.
Other reported associations of coffee drinking with cancer have
been scattered and inconsistent. Martinez (1969) found an association
between oral and esophageal cancers combined and consumption of hot
beverages, mostly coffee, whereas Stocks (1970) did not find a signifi-
cant correlation between coffee consumption and esophageal cancer.
Shennan (1973) reported a direct correlation between per capita coffee
intake and mortality from renal carcinoma (r=0.8), and the association,
though less strong, appeared also in the correlational data of Armstrong
and Doll (1975). On the other hand, case-control studies of renal can-
cer (Armstrong et^ al . , 1976; Wynder et^ al . , 1974) have not confirmed
this association. Stocks (1970) also found a direct correlation of
prostate cancer mortality with per capita coffee intake. This finding
did not appear in a similar analysis by Armstrong and Doll (1975), who
reported an association with per capita fat intake and a high correla-
tion between these two dietary factors.
Experimental Evidence; Carcinogenicity. Sprague-Dawley rats were
fed a diet containing 5% instant coffee for 2 years. No bladder tumors
were noted in rats fed diets containing the equivalent of up to 85 cups
of coffee per day (Zeitlin, 1972).
Maximum tolerated doses of regular and decaffeinated instant coffees
(6% of the diet) fed to Sprague-Dawley rats for 2 years produced no
evidence of carcinogenesis (Wttrzner eit al. , 1977). The authors also
12-14
reported that high levels of caffeine led to a lower incidence of
tumors. However, Challis and Bartlett (1975) reported that readily
oxidized phenolic compounds which are constituents of coffee cata-
lyze nitrosamlne formation from nitrite and secondary amines at gastric
pH. For example, these experiments showed that 4-methylcatechol and
the phenolic component of chlorogenic acid (approximately 13% of the
dry weight of the soluble constituents of coffee), exerted catalytic
effects on nitrosamine formation. This finding implies that several
foodstuffs and beverages, including coffee, may have cocarcinogenic
properties.
Experimental Evidence; Mutagenicity. Coffee is mutagenic to
Salmonella typhlmurium strain TA100, whether it is brewed, instant, or
decaffeinated (Aeschbacher and Wtlrzner, 1980; Aeschbacher ejL^ al. , 1980;
Nagao t_ al. , 1979). Although caffeine has been reported to be muta-
genic to^ bacteria (Clarke and Wade, 1975; Demerec e al . , 1948, 1951;
Gezelius and Fries, 1952; Glass and Novick, 1959; Johnson and Bach,
1965; Kubitschek and Bendigkeit, 1958, 1964; Novick, 1956), it could
not have been responsible for the mutagenicity of coffee observed in
these reports, since decaffeinated coffee was as mutagenic as regular
coffee and caffeine itself was not detected as a mutagen under the test
conditions used (Aeschbacher et al., 1980; Nagao et al. f 1979).
Me t hy Ixant hine s
Experimental Evidence; CarcInQgenicIty. Another widely consumed
class of compounds are the methylxanthines, which include caffeine.
There appear to be no published studies on the carcinogenicity of
caffeine in laboratory animals following chronic oral administration.
In one as yet unpublished study (Takayama, personal communication),
Wistar rats were divided into three dose groups each containing 50
males and 50 females. The first two groups were given 0.2% and 0.1%
caffeine in their drinking water for 18 months beginning at the age
of 8 weeks. Then, normal water without caffeine was given to the
surviving animals for an additional 6 months. The third group, which
served as the control group, was given normal water throughout the
experiment. All remaining animals were sacrificed 24 months after the
caffeine treatment had begun. The investigators concluded that there
was no significant increase in the Incidence of any type of tumors In \
caffeine-treated animals, as compared to control animals.
Experimental Evidence: Mutagenicity. The methylxanthines a
class of compounds that are present in tea and coffee are mutagenic
in at least some test systems. Three of the compounds caffeine,
theophylline, and theobromlne have been reported to be mutagenic to
bacteria and to cause abnormalities in the chromosomes of plant cells
(see reviews by Kihlman, 1977, and Timson, 1975). However, the muta-
genic effects of these compounds in mammals have not been clearly
12-15
demonstrated in vivo . Caffeine can enhance the genetic effects of
other chemicals, even in vivo (Frei and Venitt, 1975; Jenssen and
Ramel, 1978). This activity is presumably due to the ability of
caffeine to inhibit repair of DNA damage caused by chemical mutagens.
Cycasin
Cycasin (methylazoxymethanol-3-glucoside) is one of the most potent
carcinogens found in plants (International Agency for Research on
Cancer, 1976; Magee t al . , 1976). This compound and at least one
related glucoside (macrozamin) are present in the palmlike cycad trees
of the family Cycadaceae. These trees have provided food for natives
and their livestock in tropical and subtropical regions. The sliced
nuts are generally extracted with water prior to use, but acute
poisonings have been reported.
In Guam and Okinawa, which have high rates of liver cancer, the
ingestion of cycasin in cycad nuts has been proposed as an etiologic
factor. However, in a descriptive study conducted in the Miyako
Islands of Okinawa, investigators found no correlation between mor-
tality from hepatoma and the ingestion of cycad nuts (Hirono et a 1 ,
1970). Therefore, there is no evidence for the carcinogenicity of
cycasin in humans.
Experimental Evidence : Carcinogenicity . When administered orally,
cycasin is highly carcinogenic in the liver, kidney, and colon of rats,
and also induces tumors in other species (Laquer and Spatz, 1968). The
tissues of rats contain low levels of P-glucosidase, which hydrolyzes
cycasin. However, the hydrolysis generally depends on the action of
intestinal bacteria (Matsumoto e al_. , 1972). The product, methylazoxy-
methanol (MAM) , decomposes at neutral pH to an electrophilic intermedi-
ate that methylates nucleic acids and proteins both in vitro and in
vivo (Matsumoto and Higa, 1966). These findings and the carcinogenic
activity of MAM (Laquer and Spatz, 1968) have implicated MAM as a
proximate carcinogenic metabolite of cycasin. The methylating species
formed from MAM and- cycasin appears to be similar or identical to that
formed during the metabolic activation of the synthetic carcinogen
nitrosodimethylamine, which has carcinogenic properties similar to
those of cycasin (Magee et aj. , 1976).
Experimental Evidence; Mutagenicity. Cycasin was not mutagenic
in the standard Ames test (Ames et_ l. , 1975), but it became mutagenic
when preincubated with almond 3-glucosidase (Matsushima ! 1979).
Thiourea
Thiourea occurs naturally in laburnum shrubs and in certain fungi
(e.g., Verticillium albo-atrum and Bortrylio cinerea).
12-16
Experimental Evidence: Carcinogenicity. Thiourea has been shown
to cause thyroid tumors, hepatic adenomas, and epidermoid carcinomas of
Zymbal's gland when administered to rats as 0.2% of the drinking water
or diet for as long as 2 years (International Agency for Research on
Cancer, 1974).
Experimental Evidence; Mutagenicity. Thiourea was negative in the
standard Ames Salmonella/microsome assay (Simmon, 1979), but positive
in the host-mediated assay (Simmon et_ al_. , 1979). It also induced
transformations in hamster embryo cells (Pienta, 1981).
Tannic Acid and Tannins
Tannins are contained in many plants. These compounds are divided
into two groups the nonhydrolyzable condensed tannins and the hydrolyz-
able tannins, which are subdivided into ellagitannins or gallotannins .
Commercially, the term tannic acid generally applies to hydrolyzable
gallotannins, including taratannic acid. Tannins are widely distributed
in plants, and are present naturally in small amounts in coffee and
tea. Tannic acid has also been used by U.S. food processors as a
clarifying agent in the brewing and wine industries and as a flavoring
agent in such products as butter, caramel, fruit, brandy, maple, syrup,
and nuts (National Academy of Sciences, 1965).
Experimental Evidence; Carcinogenicity. The investigations of
Korpassy showed that subcutaneous administration of tannic acid in
doses of 150 to 200 mg/kg bw^ produced skin necrosis, ulcers, and
hepatic tumors in rats (Korpassy, 1959, 1961; Korpassy and Mosonyi,
1950, 1951). No adequate studies have been conducted to test the
carcinogenicity of orally administered tannins.
In mice, repeated subcutaneous injections of three condensed non-
hydrolyzable tannins produced liver tumors and sarcomas (Kirby, 1960).
Experimental Evidence; Mutagenicity. Tannic acid was found not to
be geno toxic or mutagenic to Saccharomyces cerevlsiae D4 and Ames ^.
typhimurium strains with and without metabolic activation (Litton
Bionetics, Inc., 1975). Tannins from various sources such as apple
juice, grape juice, wine, and betel nuts were found to be strongly
clastogenic for Chinese hamster ovary cells, but they lacked the
capacity to induce mutations in the Ames test (Stitch and Powrie, in
press) .
Coumarin
Coumarin is present in a number of plants, including tonka beans,
cassia, and woodruff, and in their essential oils (International Agency
for Research on Cancer, 1976).
12-17
Experimental Evidence: Carcinogenicity. Coumarin (cr-hydroxycinna-
mic acid-6-lactone) has induced bile duct carcinomas in rats fed 0.35%
to 0.5% of the compound in the diet for approximately 18 months.
Experimental Evidence: Mutagenicity. Coumarin was negative in the
E. coli pol A assay (Rosenkranz and Leifer, 1981). It interferes with
excision repair processes in ultraviolet-damaged DNA and with host cell
reactivation of ultraviolet-irradiated phage Tl in E_. coli WP2 (Grigg,
1972).
Parasorbic Acid
Parasorbic acid occurs in concentrations ranging from 0.2 to 2
Vtg/g in the ripe berries of the Moravian mountain ash Sorbus aucuparia
var. edulis. It has not been found in a number of common fruits
(pears, apples, lemons, cranberries, grapes, oranges, or tomatoes)
(International Agency for Research on Cancer, 1976).
Experimental Evidence: Carcinogenicity. Sarcomas resulted within
2 years in rats that had received repeated subcutaneous injections of
parasorbic acid in total doses of either 13 or 128 mg per animal
(International Agency for Research on Cancer, 1976).
Experimental Evidence; Mutagenicity. No studies concerning the
mutagenicity of parasorbic acid could be identified.
METABOLITES OF ANIMAL ORIGIN
Tryptophan and Its Metabolites
Experimental Evidence; Carcinogenicity. Dogs fed high levels of
tryptophan (7 g/day, l-eT, I times the amount fed to controls for long
periods developed hyperplasia of the urinary bladder (Radomskl e . ,
1971). When tryptophan was given to rats as 2% of the diet after sub-
carcinogenic doses of a nitrofuran, tryptophan exerted a Promoting
effect on the formation of tumors in the urinary bladder (Cohen et al. ,
W79)! In other studies, four metabolites of tryptophan ( 3-hydroxyky-
nurenlne, 3-hydroxyanthranilic acid, 2-amino-3-hydroxyacetophenone , and
xantnu'nic acid-methyl ether) each induced bl *f J^/^
implanted as pellets in the urinary bladders of mice (Clay son and
Srner 1976)! However, attempts to relate the development of tumors
the' urinary ladder of humans to abnormalities inthe metabolism of
tryptophan have not been definitive (Clayson and Gamer, 1976).
Experimental Evidence: Mutagenicity,. Tryptophan and "Bijetabo-
litefwere not mutagenic in the Salmonella/microsome assay (Bowden et
al., 1976).
12-18
Hormones
Experimental Evidence; Carcinogenicity. A number of endogenous
peptide and steroid hormones facilitate the development of tumors of
the endocrine glands of laboratory animals (Clifton and Sridharan,
1975; Furth, 1975). However, because humans consume only very small
amounts of hormones from the tissues of animals and because there is no
indication that hormones from food sources are significant factors in
the development of cancer in humans, they are not considered in this
report. One exception is diethylstilbestrol (DES), which is discussed
in Chapter 14.
FERMENTATION PRODUCT
Ethyl Carbamate (Urethan)
Ethyl carbamate, or urethan, is a fermentation product. The detec-
tion of low levels of ethyl carbamate in wines treated with the synthe-
tic sterilant diethyl pyrocarbonate (Ehrenberg t_ ad. , 1976) led to
investigations into the natural occurrence of ethyl carbamate. These
studies have demonstrated that naturally fermented foods and beverages
(e.g., wines, bread, beers, and yogurt) contain detectable, but very
low levels of ethyl carbamate, usually less than 5 }jg/kg. The ethyl
carbamate probably results from the reaction of ethanol and carbamoyl
phosphate both normal metabolic products in the yeast (Ough, 1976).
Experimental Evidence; Carcinogenicity . For, many years, ethyl
carbamate has been studied as a synthetic carcinogen in the rat, mouse,
and hamster. Its ability to induce tumors has been demonstrated by
administering the compound during the prenatal and preweanling periods
as well as to adult animals. Ethyl carbamate is active when adminis-
tered orally, by inhalation, or by subcutaneous or intraperitoneal
injection. The susceptible tissues include the lungs, lymphoid tissue,
skin, liver, mammary gland, and Zymbal's gland. Most frequently,
tumors are induced with doses ranging from 0.5 to 3 mg/g bw (Interna-
tional Agency for Research on Cancer, 1974; Mirvish, 1968). However,
lung adenomas were induced in mice with a single dose of 0.01 mg/g bw
(Nomura, 1975).
The significance of naturally occurring ethyl carbamate in foods in
the development of human cancer is unknown, but the levels are very low
in comparison to those used to induce tumors in laboratory animals
(i.e., the consumption of 5 yg/day by a 70-kg person would provide an
annual intake of approximately 0.05 yg/g bw) .
Experimental Evidence: Mutagenicity* Urethan was not !__-_
to Ames Salmonella strains (Simmon, 1979) or in the host-mediated assay
(Simmon et^ l . , 1979). However, it did induce transformations in ham-
ster embryo~cells (Pienta, 1981).
12-19
NITRATE, NITRITE, AND N-NITRQSO COMPOUNDS
Because many N-nitrosodialkylamin.es, N-nitrosoalkylamides, and
Nj-nitrosoalkylimides are strong carcinogens under a variety of condi-
tions and in many species (Magee and Barnes, 1967; Magee et^ ad. , 1976)
and because certain N-nitroso compounds have been detected in foods, in
gastrointestinal contents, and in blood or urine (Fine et_ aJ , 1977;
Hicks et.al*, 1977; Sen et ad. , 1980; Spiegelhalder et al. , 1980;
Stephany and Schuller, 1980), there has been much concern during the
past 10 to 15 years about the role of N-nitroso compounds in the eti-
ology of human cancer.
In recent years, a number of observations have also led to concern
about potential risks to human health resulting from the use of nitrate
and nitrite as preservatives in meats and other cured products. Nitrate
can be reduced to nitrite, which can interact with dietary substrates
such as amines or amides to produce N-nitroso compounds. Because the
health effects of nitrate, nitrite, and N-nitroso compounds have been
reviewed in depth by the Committee on Nitrite and Alternative Curing
Agents in Food (National Academy of Sciences, 1981), only a brief
summary is presented in this section.
Nitrate and nitrite are widely distributed in foods in varying
concentrations, depending on a number of factors such as agricultural
practices and storage conditions. It is difficult to estimate with
any precision the exposure of humans to these ions because of differing
lifestyles and dietary habits and the limitations in analytical tech-
niques for measuring them and in the methods for determining food con-
sumption. The Committee on Nitrite and Alternative Curing Agents in
Food estimated that the average U.S. diet provides approximately 75 mg
of nitrate and 0.8 mg of nitrite daily (National Academy of Sciences,
1981). Vegetables contribute most of the nitrate ingested. Other
dietary sources include nitrate-rich drinking water and fruit juices.
More than one-third of the average daily intake of nitrite is contrib-
uted by the ingest Ion of cured meats, approximately one-third by baked
goods and cereals, and less than one-fifth by vegetables.
Two additional factors must be considered when determining expo-
sure to nitrate and nitrite: Vegetables contain both inhibitors (e.g.,
ascorbic acid) and catalysts (e.g., phenols) of nitrosatlon reactions.
These modifiers tend to affect the extent of in vivo nitrosation and,
thus, the synthesis of N-nitroso compounds. Evidence Indicates that
* n vivo nitrosation occurs when amines and/ or amides and nitrate and/
or nitrite are ingested simultaneously (National Academy of Sciences,
1981). The key factors that determine the extent of these reactions
in the stomach are the gastric pH; the concentrations of the nitrate
and/or nitrite and the nitrosatable amines and/or amides; the rates of
nitrosation of the substrate; and types and amounts of nitrosation
modifiers in the stomach.
12-20
Humans may also be exposed to preformed nitrosamines that occur
as contaminants In some foods, chiefly in nitrate- or nitrite-treated
products ( Gough et_ al^. , 1978; Spiegelhalder e al. , 1980; Stephany and
Schuller, 1980). The largest single dietary source of nitrosamines
was beer until recently, when maltsters reduced the concentrations by
modifying the malting processes. The most important sources of nitros-
amines in the diet are now cured meat products, especially bacon, which
contributes approximately 0.17 yg of nitrosopyrrolidine per person
daily. In the United States, the Intake of nitrosamines from all
dietary sources, including beer, is estimated to be approximately 1.1
yg/day.
Nitrate can be converted to nitrite by bacterial reduction in the
saliva. Roughly 25% of Ingested nitrate is recirculated into saliva,
and approximately 20% of salivary nitrate is reduced to nitrite
(National Academy of Sciences, 1981).
The formation of nitrate by bacteria in the large intestine
(heterotrophic nitrification) has been postulated as one mechanism to
account for differences in ingestion and urinary excretion of nitrate
by humans ( Tannenbaum et_ al. , 1978). However, these conclusions appear
to be eirroneous since studies in germfree rodents indicate that such
reactions are not important ( Green e al. , 1981). Moreover, the nitrate
content of ingested food, water, and air may have been underestimated
in the earlier studies. Recent studies suggest that mammalian tissues
synthesize nitrate and that this may partially explain excess urinary
nitrate excretion (Green e al. , 1981; Parks e al. , 1981). However,
the amount of nitrate produced endogenously appears to be less than
that suggested in earlier studies by Tannenbaum e al. (1978).
The formation of N-nitroso compounds in vivo has been well docu-
mented in laboratory animals (Mirvish et al., 1980). In humans, the
evidence is sparse. However, one recent study provides direct evidence
that nitrosamines are synthesized in humans following the ingestion of
an amine (proline) and nitrate (Ohshima and Bartsch, 1981). In that
experiment, the ingestion of a large excess of ascorbic acid or a-
tocopherol effectively reduced the endogenous formation of nitrosa-
mines.
Epidemiological Evidence
Studies conducted in Colombia, Chile, Japan, Iran, China, England,
and the United States (Hawaii) have indicated that there is an associa-
tion between Increased incidence of cancers of the stomach and the
esophagus and exposures to high levels of nitrate or nitrite In the
diet or drinking water. (See, for example, Armijo and Coulson, 1975;
Armijo e auL . , 1981; Correa e al. , 1975; Cuello et al., 1976; Haenszel
et al. , 1972; Higginson, 1966; Meinsma, 1964). ~
12-21
Exposures to nitrate, nitrite, or N-nitroso compounds were not
directly measured in these epidemiological studies. The associations
with cancer were based either on correlations of high risk population
groups with corresponding exposures in food and water supplies, or on
comparisons of the frequency of consumption of foods containing these
substances (plus secondary amines) by gastric cancer patients and by
controls*
Bladder cancer has been correlated with nitrate in the water
supply or with urinary tract infections in some epidemiological studies
(Howe et^ al. , 1980; Wynder ejt al . , 1963). However, Howe et_ al . (1980)
reported that there was no difference between cases and controls in
consumption of nitrite-preserved meats, such as hams and sausages.
Nevertheless, it is of interest that nitrosamines, which are presumably
formed from dietary precursors, have been found in the urine of patients
with urinary tract infections and could presumably be carcinogenic in
the bladder (Hicks et ad. , 1977; Radomski e al. , 1978).
The Committee on Nitrite and Alternative Curing Agents in Food
concluded that these reports do not provide conclusive evidence of a
causal relationship, and that alternative explanations for the find-
ings have not been ruled out (National Academy of Sciences, 1981).
Studies of occupational exposure have not contributed significant
information on possible associations between N-nitroso compounds and
cancer risk.
Experimental Evidence; Carcinogenicity
The data on the carcinogenicity of nitrate and nitrite in animals
are not definitive. The few experiments conducted in animals have
provided no evidence that nitrate is carcinogenic (Greenblatt and
Mirvish, 1973; Lijinsky et ail. , 1973; Sugiyama e aJ. , 1979).
There have been very few adequate studies to test the carcinogenic-
ity of nitrite. Most of the information is derived from data on tumor
incidence in experiments that were designed primarily to study nitrosa-
tion in animals given nitrite and amine simultaneously. These data
were compared with data on control animals given nitrite alone (usually
in drinking water). Because the control animals were usually sacrificed
after a few months, there may not have been sufficient time for tumors
to develop (Aoyagi et^ al . , 1980; Inai e aJ . , 1979; Mirvish et al.,
1980; Shank and Newberne, 1976).
In a larger lifetime study conducted for the U.S. Food and Drug
Administration, Newberne (1978, 1979) fe4 various doses of nitrite to
groups of approximately 68 male and 68 female Sprague-Dawley rats under
a variety of conditions. In comparison to the controls, the treated
12-22
rats had not only a higher incidence of malignant tumors of the lympha-
tic system, but also a higher incidence of alterations (immunoblastic
cell proliferation) in the spleen and, occasionally, in the lymph nodes
of the treated groups (Newberne, 1979). These results were interpreted
by the author to indicate that nitrite may be an enhancer or promoter
of carcinogenesis in rats. However, a Joint Committee of Experts, which
was established to review the study, diagnosed fewer lymphomas than
those reported by Newberne (U.S. Food and Drug Administration, 1980a).
The discrepancy between the two diagnoses involved the differentiation
of lymphomas from extramedullary hematopoiesis, plasmacytosis, or his-
tiocytic sarcoma. Furthermore, the Joint Committee was unable to con-
firm the diagnosis of inununoblastic hyperplasia.
In addition, the Committee on Nitrite and Alternative Curing Agents
in Food reviewed 21 reports in which the carcinogenicity of nitrite was
examined (National Academy of Sciences, 1981). The committee concluded
that three of the 21 reports were too brief to evaluate adequately. Of
the remaining 18 studies, 9 were conducted in rats, 8 in mice, and 1 in
guinea pigs. The experimental design was inadequate in many cases, and
varied greatly with regard to the end points for carcinogenicity. How-
ever, none of the remaining 18 studies provided sufficient evidence
that nitrite was carcinogenic (see, for example, Greenblatt et al.,
1973; Lijinsky jet al. , 1980).
The absence of evidence that nitrite is a direct carcinogen does
not diminish the possibility that it can interact with specific compo-
nents of diets consumed by humans and animals or with endogenous metab-
olites to produce N-nitroso compounds that induce cancer.
Nj-Nitroso compounds have been studied extensively to determine
their carcinogenic effects. Druckrey and his colleagues (1967)
reported tests in rats exposed to 65 N-nitroso compounds, most of
which were potent carcinogens. Lijinsky and Reuber (1981) examined
many other N-nitroso compounds for their carcinogenic potential, mainly
in rats. Approximately 300 different N-nitroso compounds have been
tested, and a majority of them have been shown to induce cancer in
various tissues of one or more species of laboratory animals when
administered by any of several routes (Preussmann and Steward, personal
communication, 1981). In addition to both nitrosodimethylamine and
nitrosodiethylamine, a number of other N-nitroso compounds detected
in the environment are carcinogenic in animals (see, for example,
Druckrey et al. , 1967; Preussmann e al. , 1981).
The carcinogenic action of several N-nitroso compounds can be
inhibited in systems where the formation of N-nitroso compounds has
been prevented (Mirvish, 1981). Nitrosation is inhibited when ascorbic
acid and a variety of other agents compete with the mitiosattable agent
for the available nitrite in the acidic conditions of the stomach. A
number of other agents that interact readily with nitrite can inhibit
nitrosation. Among these are other isomers of ascorbic acid^ sorbic
12-23
acid, some phenols, and ot-tocopherol* Most of these interactions have
been observed at the chemical rather than at the biological level.
Formation of Nf nitroso compounds can also be enhanced since a
variety of ions, especially thiocyanate and iodide, may catalyze the
nitrosation reaction in the stomach (Mirvish et al * , 1975). Since
these ions are present in foodstuffs, these catalysts could be
important in determining the outcome.
The additive or synergistic effects of Jfl-nitroso compounds on other
carcinogens with similar organotropy has been emphasized by SchmShl
(1980).
Experimental Evidence: Mutagenicity
Nitrate does not appear to be directly mutagenic (Konetzka, 1974).
In microbial systems, nitrite may be mutagenic by three different
mechanisms (Zimmerman, 1977): deamination of DNA bases in single-
stranded DNA; formation of 2-nitroinosine, intrastrand, or inters trand
lesions leading to helix distortions in double-stranded DNA; and forma-
tion of mutagenic N~-nitroso compounds by combination with nitrosatable
substrates. Except for the results of one study in which a high dose
of nitrite was used, there is no evidence that nitrite is mutagenic in
mammalian systems. ^
Many N-nitroso compounds have been found to be mutagenic in a
variety of test systems, including bacterial tests and Drosophila, and
under a variety of conditions (Montesano and Bartsch, 1976).
Summary and Conclusions: Nitrate, Nitrite, and Jfl-Nitroso Compounds
Epidemiological evidence suggesting that nitrate, nitrite, and
N-nitroso compounds play a role in the development of cancer in humans
is largely circumstantial. However, the findings from several epidem-
iological studies of certain geographical/nationality groups are con-
sistent with the hypothesis that exposure of humans to high levels of
nitrate and/or nitrite may be associated with an increased incidence of
cancers of the stomach and esophagus. In. these studies, the level,
duration, and time of exposure were not studied in relation to cancer
incidence, and exposure to other known or. suspected carcinogens was not
excluded.
In animals, nitrate has not been shown to be carcinogenic or muta-
genic per se The data on nitrite, which has been tested more exten-
sivelyHEKan nitrate, indicate that nitrite is probably not carcinogenic
but that it is mutagenic, at least in microbial systems.
12-24
As a group, the N-nitroso compounds are clearly carcinogenic in
numerous species of animals in which they have been tested. Positive
results have been obtained for nearly all of the approximately 300
N-nitroso compounds tested for carcinogenicity in one or more species*
Many of these compounds are also mutagenic.
The Committee on Nitrite and Alternative Curing Agents in Food
recommended that exposure to nitrate, nitrite, and N-nitroso compounds
should be reduced (National Academy of Sciences, 1981).
SUMMARY AND CONCLUSIONS
This chapter contains an assessment of the carcinogenicity and
mutagenicity of some naturally occurring substances, mainly mycotoxins
and compounds of plant origin.
Aflatoxin, a mycotoxin that occurs in grains and other food com-
modities, is carcinogenic in several species of animals, including
mice, rats, trout, ducks, and monkeys, and there is evidence of a dose
response. In addition, it has been shown to be mutagenic in bacterial
and mammalian systems. Several other mycotoxins that are found in food
are carcinogenic and/or mutagenic in laboratory tests. However, with
the exception of aflatoxin, which has been implicated in liver cancer
in some parts of the world, there is no epidemiological evidence con-
cerning other mycotoxins and neoplasia in humans.
Hydrazine derivatives of two mushrooms Agaricus bisporus and
Gyromitra esculent a both of which are consumed throughout the world,
appear to be carcinogenic in mice and, under certain conditions/ in
hamsters, and are mutagenic in bacteria. However, the significance of
these findings for risk to humans cannot be determined since there are
no epidemiological data.
Several pyrrolizidine alkaloids, e.g., monocrotaline, are
carcinogenic in animals and/or mutagenic in several test systems.
Tumors develop in rats fed plants such as coltsfoot, which contain
these alkaloids. Cycad nuts, which are eaten in some parts of the
world, contain cycasin (methylazoxymethanol-3-glucoside) , a compound
known to be carcinogenic in animals. It is also mutagenic in the Ames
test after addition of $-glucosidase. However, no evidence has been
presented for the carcinogenicity of pyrrolizidine alkaloids and
cycasin in humans, although there is unsubstantiated speculation that
they may be involved in the development of neoplasia in humans.
Other plant constituents, such as methylxanthines, thiourea,
tannins, coumarin, parasorbic acid, safrole, estragole, and eugenol,
and plant estrogens, such as zearalenone, are carcinogenic in labora-
tory animals and/or mutagenic in bacterial or mammalian cell systems.
However, the significance of these findings for human health is not
known since there are no data from studies in humans.
12-25
Nitrosamin.es compounds derived from the reaction of nitrite with
amines are carcinogenic in numerous species of laboratory animals and
mutagenic in several experimental systems. Nitrate appears to be
neither carcinogenic nor mutagenic, whereas nitrite is probably not
directly carcinogenic, but it is mutagenic in microbial systems. There
is some inconclusive epidemiological evidence that nitrate, nitrite,
and N-nitroso compounds play a role in the development of gastric and
esophageal cancer.
Many of the naturally occurring substances discussed in this
chapter have been found to be carcinogenic in laboratory animals and/
or mutagenic in bacterial and other systems, thereby posing a potential
risk of cancer in humans. However, there have been no pertinent epi-
demiological studies concerning their impact on -humans except for those
on aflatoxins and those on nitrate, nitrite, and N-nitroso compounds.
The compounds thus far shown to be carcinogenic in animals have been
reported to occur in the average U.S. diet in small amounts; however,
there is no evidence that any of these substances individually makes a
major contribution to the total risk of cancer in the United States.
This lack of sufficient data should not be interpreted as an indication
that these or other compounds subsequently found to be carcinogenic do
not present a hazard. Further investigations are necessary. Efforts
should be made to minimize or avoid the exposure of humans to compounds
that are carcinogenic or mutagenic in experimental systems.
12-26
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Lancet 1:1066.
Zimmerman, F. K. 1977. Genetic effects -of nitrous acid. Mutat. Res.
39:127-147.
CHAPTER 13
MUTAGENS IN FOOD
As interest in the possible relationship between diet and cancer
has increased in recent years, so have attempts to determine whether
chemical carcinogens may be present in our foods. The foods that we
eat contain a vast number of separate chemical entities: several
thousand as additives and many times this number as natural constitu-
ents. Of course, most of these chemicals are present in relatively
low concentrations, but if potent carcinogens exist, even at low con-
centrations in commonly consumed foods, they may warrant concern. The
problem, therefore, is how to test the very large number of chemicals
present in the complex mixtures we call food to determine whether or
not they may be contributing to our risk for cancer. An adequately
performed chronic feeding study in rodents to determine whether a
chemical is a carcinogen takes several years to complete and analyze
and can cost more than $500, 000. Therefore, the use of simpler and
less expensive tests may be considered, at least to help us determine
which chemicals to subject to long-term studies.
As discussed elsewhere in this report, initiation of the carcino-
genic process may involve an alteration in the genetic material of a
cell. Therefore, it is reasonable to suppose that chemicals that
alter DNA (e.g., cause mutations) will have a high probability of
being initiators of carcinogenesis. The fact that DNA is chemically
similar in all living organisms means that even chemicals that cause
mutations in bacteria can be suspected as potential carcinogens in
humans. In several extensive studies conducted in independent lab-
oratories, the correlations between mutagenic activity in bacteria
and carcinogenicity in mammals have been analyzed (McCann and Ames,
1976; McCann eit l. , 1975; Purchase et al. , 1978; Simmon, 1979;
Sugimura et_ al . , 1976). It is clear from these and other studies
that a chemical found to be mutagenic in any living system should
be suspected of being carcinogenic. However, it is impossible to
provide a single number to express the degree of confidence with
which a mutagen can be considered to be a carcinogen or with which
a nonmutagen can be regarded as a noncarcinogen. This uncertainty
arises from several sources, the most important of which is that the
correlation between mutagenicity and carcinogenicity is highly de-
pendent upon the class of chemical being investigated. For some
classes of chemical carcinogens, such as aromatic amines, polycyclic
hydrocarbons, and direct alkylating agents, there appears to be a
high degree of correlation. However, it is difficult to detect the
mutagenic activity of some types of carcinogens, especially highly
chlorinated compounds. Therefore, judgment must be exercised, in-
cluding a careful consideration of the structure and likely metabo-
lites of the chemical under test, when the significance of a positive
or negative mutagenicity test is being evaluated.
13-2
The utility of mutagenicity tests in identifying chemical carcino-
gens and the subsequent removal of these compounds from products to
which humans are exposed can be illustrated by several historical ex-
amples. These would include the food preservatives 2-(2-furyl)-3-
(5-nitrofuryl)acrylamide (AF-2), which was extensively used in Japan,
the flame retardant chemical tris(2,3~dibromopropyl)phosphate, which
was widely used in children's sleepwear in the United States, and the
hair dye ingredient 2,4-diaminoanisole. The fact that simple muta-
genicity tests correctly predicted the carcinogenic potential of these
chemicals adds to our confidence that correctly interpreted muta-
genicity data can assist us in identifying environmental carcinogens.
The most widely used of the mutagenicity assays is the Salmonella
plate incorporation test, commonly known as the Ames test. In this
assay, a chemical is tested for its ability to induce mutations in
different strains of a bacterium ( Salmonella typhimurium) Most
chemical carcinogens and mutagens do not interact directly with DNA.
They require alteration by enzymes in order to become activated. This
process of "metabolic activation" cannot usually be accomplished by
enzymes present in bacteria. Therefore, in the Salmonella test, an
extract of mammalian liver (usually from the rat) is added to provide
the enzymes necessary for metabolic activation.
Many mutagenic test systems other than $_ typhimurium have been
used to test chemicals (see review by Hollstein and McCann, 1979). In
the discussion that follows, however, most of the studies discussed
involve S^. typhimurium. Mutagenicity assays have also been used to
investigate the interactions between chemicals. This has resulted in
the discovery of both comutagens, which enhance mutagenic activity of
other chemicals, and inhibitors of mutagenesis. The knowledge that a
chemical is a comutagen or an inhibitor of mutagenesis can provide us
with a useful tool for investigating the metabolic fate and genetic
interactions of chemicals. Modification of mutagenic activity, par-
ticularly as determined in in vitro test systems, frequently has no
relevance to in vivo effects. Specific in vitro effects of modifiers
of mutagenesis, such as inhibition of a particular metabolizing enzyme,
for example, may not operate or may even have the opposite effect in
living organisms. However, where modification of mutagenesis is ob-
served, the mechanism should be elucidated.
MUTAGENS RESULTING FROM COOKING OF FOODS
Benzo[&]pyrene and Other Polynuclear Aromatic Hydrocarbons
Almost 20 years ago Lijinsky and Shubik (1964) and Seppilli and
Sforzolini (1963) reported that beef grilled over a gas or charcoal
fire contained a variety of polycyclic aromatic hydrocarbons (PAH f s).
Benzo[ajpyrene was found in charcoal-broiled steak in levels up to 8
US/kg (Lijinsky and Shubik, 1964). The source of the PAH's resulting
13-3
from charcoal broiling was the smoke generated when pyrolyzed fat
dripped from the meat onto the hot coals. Thus, meats with the highest
fat content acquired the highest levels of these chemicals (Lijinsky
and Ross, 1967). When meat was cooked in a manner that prevented expo-
sure to the smoke generated by the dripping fat, this source of contam-
ination was either reduced or eliminated (Lijinsky and Ross, 1967;
Lintas e al. , 1979; Masuda et_ al. , 1966).
PAH's have also been found in a variety of smoked foods and in
roasted coffee (Howard and Fazio, 1980). Vegetables can easily become
contaminated by PAH f s from air, soil, or water; fish and shellfish can
assimilate such chemicals from their marine environments (Howard and
Fazio, 1980). However, unless vegetables or seafood are obtained from
highly contaminated environments, the major source of PAH will probably
be the smoking or cooking of food.
Mutagens from Pyrolyzed Proteins and Ainino Acids
During the past few years, it has become clear that PAH's account
for only a small fraction of the mutagenic (and, therefore, potentially
carcinogenic) activity that occurs in foods during cooking* Nagao et
a 1 . (1977a) used dimethylsulf oxide to prepare extracts of the charred
surfaces of broiled fish and meat. They found that the mutagenic acti-
vities of these extracts for histidine-requiring strains of S^ typhi-
murium were hundreds or thousands of times greater than could be
accounted for by the reported benzo[a.]pyrene contents of these cooked
foods. For example, the mutagenic activity of charcoal-broiled beef-
steak was the equivalent to that of approximately 4,500 ug of benzo[aj-
pyrene per kilogram of steak, even though Lijinsky and Shubik (1964)
had reported that charcoal-broiled steak contained no more than
8 yg of this chemical per kilogram.
The mutagenic activity in the broiled fish and beef could also be
detected in S^. typhimurium strain TA98, implying that the agent could
induce frameshift mutations (Nagao et al. , 1977a; Sugimura et al. ,
1977). Positive results in these assays depended on the presence of
an iEL v ^ trQ metabolic activation system utilizing the postmitochon-
drial supernatant from homogenized livers of rats pretreated with
polychlorinated biphenyls. Bjeldanes ejt l . (in press, a, b) have re-
cently completed a series of detailed studies on the cooking condi-
tions under which mutagenic activity is produced in various types of
fish, meats (including organ meats), as well as eggs, milk, cheese,
and tofu.
To determine what constituent or constituents of fish and meat
contribute to the mutagenic activity produced by cooking, studies have
been conducted to examine the mutagenicity of smoke condensates from
various substances. Smoke obtained from pyrolyzed proteins, such as
lysozyme and his tone, was found to be highly mutagenic to S^. typhi-
murium, whereas smoke condensates from pyrolyzed DNA, RNA, starch, or
vegetable oil were only slightly mutagenic (Nagao al. , 1977b).
13-4
Pyrolysis of tryptophan resulted in more mutagenic activity than did
any other common amino acid, but almost all of the amino acids tested
yielded some mutagenic activity when pyrolyzed (Matsumoto et al.,
1977; Nagao et al. , 1977c).
Purification of the mutagenic products resulting from pyrolysis of
tryptophan resulted in the isolation of two previously unknown amino-Y-
carbolines that are potent mutagens : 3-amino-l,4 ,-dimethyl-5H~pyrido-
[4 , 3-bJindole (referred to as Trp-P-1, for "Tryptophan Pyrolysate 1")
and 3-amino-l-methyl-5H-pyrido[4,3-lb]indole (Trp-P-2) (Akimoto et al. ,
1977; Sugimura et_ l. , 1977; Takeda et_ al. , 1977).
The mutagenic activity resulting from pyrolysis of L-glutamic
acid was shown to be due to the formation of 2-amino-6-methyldipyrido-
[l,2-a.:3 f 2'-cT|imidazole (Glu-P-1) and 2-aminodipyrido[l,2-a :3 f ,2'-dJ-
imidazole (Glu-P-2) (Yatnamoto e a^. , 1978). The structural simi-
larity between these products of glutamic acid pyrolysate and Trp-P-1
and Trp-P-2 is evident from Figure 13-1.
Wakabayashi e JL. (1978) isolated a different, but structurally
related, heterocyclic mutagen from pyrolyzed lysine. This compound
was 3,4-cyclopentenopyrido[3,2-aJcarbazole (Lys-P-1). Pyrolysis of
phenylalanine resulted in the formation of the mutagen 2-amino-5-
phenylpyridine (Phe-P-1) (Sugimura et_ al. , 1977).
When soybean globulin was pyrolyzed, the substances that contrib-
uted to the mutagenic activity were compounds not previously identified
as pyrolysis products of any individual amino acid. These compounds,
2-amino-9Kh-pyrido[2,3-bJindole (AaC) and 2-amino-3-methyl-9H-pyrido-
[2,3-bJindole (MeAc^C), are quite closely related to the Y-carboline
compounds Trp-P-1 and Trp-P-2 (Yoshida t ad . , 1978).
Uyeta e al. (1979) found that both Trp-P-1 and Trp-P-2 were
present in pyrolysates of casein and gluten. Yamaguchi et^ al. (1979)
identified Glu-P-2 in the tar resulting from pyrolysis o~casein.
These investigators estimated that Glu-P-2 and Glu-P-1 accounted for
approximately 10% of the total mutagenic activity of the pyrolysate.
Analyses have confirmed that at least some of the mutagenic
pyrolysis products of amino acids are present in cooked foods. For
example, Trp-P-1 has been found in "very well done" broiled beef and
Glu-P-2 in broiled cuttlefish, although they account for less than 10%
of the total mutagenic activity in extracts of these foods (Yamaguchi
et_al., 1980a,b). Similarly, sardines broiled to a dark brown color
contain Trp-P-1, Trp-P-2, and Phe-P-1, although most of the mutagenic
activity in these fish was due to the presence of other compounds
(Yamaizumi et al. , 1980) (Table 13-1). Pieces of beef or chicken
grilled in a high gas flame contained AaC and MeAaC (Matsumoto et al. ,
1981). Similarly, AaC could be identified in grilled onions.
13-5
From Amino Acids:
CH 3
A
Tryptophan pyrolysates
N'
H
CH 3
Trp-P-1
CH 3
A
NH,
H
Trp-P-2
Glutamic acid pyrolysates
N
CH 3
Glu-P-1
Lysine pyrolysate
Lys-P-1
From Proteins:
Glu-P-2
Phenylalanine pyrolysate
NH 2
Phe-P-1
Soybean globulin pyrolysates
H
AaC
CH 3
H
MeAaC
FIGURE 13-1. Some mutagens from pyrolysates and from cooked foods.
(Figure continued on next page.)
13-6
Figure 13-1 (continued): Some mutagens from pyrolysates and from
cooked foods*
From Broiled Sardines:
N-CH 3
IQ
Protein pyrolysates
N CH,
From Broiled Beef:
Protein pyrolysate
H 3 C
N CH 3
MelQx
Two previously unknown mutagens were isolated from broiled sardines
(Kasai e a]L. , 1979). These were 2-amino-3-methylimidazo[4,5-f ]quino-
line (IQ) and 2~amino-3,4-dimethylimidazo[4,5~]quinoline (MelQ) , which
are extraordinarily potent mutagens to S* typhimurium strain TA98
(Kasai e ad. , 1980a,b,c). Except for the beef that contained IQ and
possibly that containing MelQ and 2-amino-3,8-dimethylimidazo-[4,5-:f ]-
quinoxaline (MelQx), the foods listed as sources of mutagens in TabTe
13-1 appear to have been very well cooked and even charred on the
surfaces to produce the mutagenic compounds identified in the table.
Information on mutagens formed by cooking foods at lower temperatures
is discussed in the next section.
As discussed in Chapter 3, the mutagenic activity of a chemical in
bacteria indicates potential genotoxicity and possible carcinogeniclty
in mammals. To test for carcinogenic activity, it is necessary to use
mammalian cell systems and intact mammals. Whenever other test systems
also indicate genotoxic activity, it is more likely that a bacterial
mutagen can act as a carcinogen.
13-7
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Four of the mutagenic pyrolysates derived from amino acids or
protein Trp-P-1, Trp-P-2, Glu-P-1, and AaC have been shown to in-
duce sister chromatid exchanges in a permanent line of human lympho-
blastoid cells (Tohda jat al. , 1980). In addition, the basic fraction
extracted from pyrolyzed tryptophan was found to cause mutations re-
sulting in resistance to ouabain or 8-azaguanine in cultured Chinese
hamster lung cells (Inui et_ al. , 1980). Trp-P-1 , Trp-P-2, and Glu-
P-l can transform primary Syrian golden hamster embryo cells (Takayama
ejt_ aJU , 1977, 1979). The cells transformed by Trp-P-2 have been shown
to grow in soft agar and to result in tumors when inoculated into the
cheek pouches of young hamsters with unimpaired immunocompetence (Taka-
yama ej^ al* , 1978).* Although these findings support the potential car-
cinogenicity of these chemicals, a definitive determination of carcino-
genicity must be made in whole animals.
Several of the mutagenic pyrolysates of amino acids or proteins
have been tested for carcinogenicity in vivo, Neoplastic nodules,
which are presumed to be precancerous changes, were found in the
livers of Wistar rats given the basic fraction from pyrolyzed trypto-
phan at 0.2% in the diet (Matsukura et_ al_. , 1981b). Neither neoplas-
tic nodules nor liver tumors had previously been observed in this
strain of rats in this laboratory. Subcutaneous injection of Trp-P-1
(1.5 mg once a week for 20 weeks) induced sarcomas in Syrian golden
hamsters and in Fischer rats (Ishikawa e_t_ al_. , 1979). Trp-P-2 did not
induce tumors in either hamsters or rats under the same experimental
conditions ( Ishikawa et_ al_. , 1979). Trp-P-1 and Trp-P-2 produced
liver tumors in CDF]_ (BALB/c x DBA) mice that were fed a diet con-
taining 0.02% of either of these chemicals (Matsukura et_ al_. , 1981a) .
Some of these liver tumors metastasized to the lung. Female mice were
more susceptible to these carcinogens than were the males. Six of nine
female ACI rats fed 0.1% Trp-P-2 in their diet developed neoplastic
nodules of the liver, and one of the six developed a hemangioendothe-
lial sarcoma of the liver (Hosaka e al. , 1981). None of the control
animals developed such nodules or tumors. Glu-P-1, Glu-P-2, AaC, and
MeAaC induced hepatomas in mice. Glu-P-1 and Glu-P-2 also induced
hemangioendotheliomas between the scapulae of mice fed diets contain-
ing 0.05% of either of these chemicals (Sugimura, in press). Thus, it
appears that the identification of several of the mutagenic compounds
found in pyrolysates of proteins and amino acids was an accurate pre-
dictor of carcinogenicity. However, the presence of a carcinogenic
chemical in a pyrolyzed amino acid or protein mixture does not neces-
sarily imply that the carcinogen will also be present in normally
cooked, uncharred food.
Mutagens Formed from Meat at Lower Temperatures '
In the experiments concerning the formation of mutagenic pyrolysis
products from amino acids and proteins, temperatures of 250C or
greater were used (Matsumoto t al. , 1977; 1978; Uyeta et al. , 1979).
However, it is now known that simply boiling beef stock~t~Temperatures
13-9
of approximately 100C results in the formation of bacterial mutagens
(Commoner et_ al. , 1978; Vithayathil et^ al_ , 1978). In fact, the forma-
tion of mutagens in beef stock has been detected at temperatures as
low as 68C (Dolara et_ al . , 1979). Frying of fish at 190C produces
mutagenic activity (Krone and Iwaoka, 1981). Mutagenic activity also
results when hamburgers are broiled, even when the surface temperature
does not exceed 130C (Weisburger and Spingarn, 1979)- A portion of
the mutagenic activity formed from heated beef extract or from fried
beef was found to be due to a chemical with a molecular weight of 198
(Spingarn et_ al_. , 1980a) , which has now been shown to be IQ (Kasai et
al* , 1980a) * MelQx, another heterocyclic mutagenic compound that has
not been identified as an amino acid or protein pyrolysate, has also
been found in fried beef (Kasai ejt^ al. , 1981). However, the frying
temperature was not specified. Weisburger and Spingarn (1979)
suggested that this mutagen, formed in beef at moderate temperatures,
may result from a browning reaction between sugars and amines rather
than from the pyrolysis of proteins.
Mutagen Formation Involving Carbohydrates
If the formation of IQ during the cooking of beef results from a
browning reaction, it might be expected that the browning of starchy
foods could also result In the formation of mutagens. Spingarn et al.
(1980b) have observed that the frying of potatoes and the toasting of
bread result in the formation of mutagenic activity, but the chemi-
cal(s) responsible for this activity and their source during the
cooking process remain to be determined.
Browning of foods results from the reaction of amines with sugars.
Using a model system for the browning reaction, Spingarn and Garvie
(1979) found that mutagenic activity occurred when any of six different
sugars, including glucose, were refluxed with ammonium hydroxide. Sev-
eral laboratories have found that heating a mixture of the amino acid
lysine with glucose at temperatures between 100C and 121C results
In products that are mutagenic (Powrie !.> 1981; Shinohara et al. ,
1980; Yoshida and Okamoto, 1980). The increase in mutagenic activity
with time paralleled the increase In browning (Shinohara et_ _al : . , 1980).
Mutagenic activity could also be produced by using certain amino acids
other than lysine (Powrie e al,. , 1981; Yoshida and Okamoto, 1980) or
by using fructose rather than glucose (Powrie et_ aJ. , 1981).
Chromosome aberrations are alterations in the structures of chromo-
somes that can be observed through a microscope. Such aberrations are
not likely to be heritable. The significance of their induction in
cells in vitro Is not clear, particularly for chemicals unable to in-
duce heritable mutations or in vivo chromosome aberrations.
Pyrazine and four of its alkyl derivatives compounds formed by
heating mixtures of sugars and amino acids (Koehler et al. , 1969)
were found to be nonmutagenic to S_. typhimurium but capable of induc-
ing chromosome aberrations in cultured -Chinese hamster ovary (CHO)
13-10
cells (Stich et_ aJL. , 1980). Commercial caramel and caramelized sam-
ples of several sugars prepared by heating sugar solutions also caused
chromosome aberrations in CHO cells (Stich et^ al_. , 1981b) . Similarly,
furan and six of its derivatives, which can be produced in foods by
heating carbohydrates (Maga, 1979), were found to cause chromosome
aberrations in CHO cells but to be nonmutagenic to bacteria (Stich et
al., 1981a).
PLANT FLAVQNQIDS
Among the most widespread of the known naturally occurring mutagens
(possible carcinogens) that are normal constituents of many foods are
the mutagenic flavonoids. Among the flavonol aglycones that have been
shown to be mutagenic to S_. typhimurium are quercetin, kaempferol, and
galangin (Bjeldanes and Chang, 1977; Brown, 1980; Hardigree and Epler,
1978; MacGregor and Jurd, 1978). Quercetin has also been reported to
induce gene conversion in yeast (Hardigree and Epler, 1978), transforma-
tion of both hamster embryo cells (Umezawa ejt_ al^ , 1977) and BALB/c 3T3
mouse cells (Meltz and MacGregor, 1981) , and mutations and single-
stranded DNA breaks in L5178Y mouse cells (Meltz and MacGregor, 1981)*
Both quercetin and kaempferol have been reported to cause mutations in
V79 Chinese hamster cells (Maruta t_ alU , 1979) and heritable mutations
(sex-linked recessive lethals) in the fruit fly Drosophila melanogaster
(Watson, 1982).
In some mutagenic plant products consumed by humans, the mutagenic
substances isolated were identified as flavonoids* For example, most
of the mutagenic activity of an acid hydrolysate of green tea could be
accounted for by three flavonoids: kaempferol, quercetin, and myricetin
(Uyeta eit_ _al. , 1981). The flavonoids kaempferol and isorharanetin were
found to be responsible for most of the mutagenic activity found in Japa-
nese pickles (Takahashi ej^ l . , 1979). The mutagen in the spice of
sumac was found to be quercetin (Seino et_ al. , 1978). Isorhamnetin and
quercetin were the major mutagens in a methanol extract of dill weed
(Fukouka et al. , 1980) .
Brown (1980) reported that the edible portions of most food plants
contain flavonoid glycosides, especially quercetin and kaempferol. He
estimated that the average daily intake of flavonoids in the U.S. diet
is approximately 1 g and that the daily intake of mutagenic flavonoid
glycosides may be equivalent to approximately 50 mg of quercetin.
Approximately 25% of the flavonoid intake is derived from tea, coffee,
cocoa, fruit jams, red wine, beer, and vinegar (Brown, 1980).
In view of the mutagenic activity and widespread distribution of
certain flavonoids, particularly quercetin, it is important to deter-
mine the carcinogenic potential of these chemicals. At present, the
data concerning the carcinogenicity of quercetin are contradictory.
Pamukcu et^ al_. (1980) reported that adding 0.1% quercetin to the diet
13-11
of albino Norwegian rats for 58 weeks resulted in the induction of
tumors in the epithelium of the intestine and urinary bladder. How-
ever, when Saito et_ aJU (1980) fed 2% quercetin to ddY mice throughout
the lives of the animals, they found no significant increase in tumor
incidence. At doses as high as 10% quercetin in the diet fed through-
out life, no significant increase in tumor incidence was observed in ACI
rats (Hirono !_ , 1981) or in hamsters (Morino et_ aJU , 1982).- The
reason for the discrepancy between the findings of Pamukcu ejt al. and
the other investigators is not clear, but may relate to differences in
sensitivity among the species and strain tested.
Flavonols often exist in plants in the form of glycosides. For
example, rutin is a glycoside of quercetin that can be hydrolyzed to
release quercetin by enzymatic or chemical treatment. Such hydrolysis,
mediated by intestinal bacteria, occurs when glycosides are consumed
in foods. Rutin and other glycosides of mutagenic flavonoids have been
shown to be mutagenic to S_. typhimurium following treatment with glyco-
sidase-containing extracts of the mold Aspergillus niger (Nagao et^ al. ,
1981), the snail Helix pomatia (Brown and Dietrich, 1979), rat cecal
contents (Brown and Dietrich, 1979), or human feces (Tamura et al. ,
1980). Mutagenic activity of rutin has also been reported in S^ typhi-
murium in the absence of glycosidase treatment, but only at doses higher
than those required when such treatment is used (Hardigree and Epler,
1978).
MUTAGENIC ACTIVITY IN EXTRACTS OF FOODS AND BEVERAGES
Several food substances have been reported to contain mutagenic
activity, although the specific chemicals responsible for this activity
have not yet been identified. For example, coffee is mutagenic to
Salmonella typhimurium strain TA100, whether it is brewed, instant, or
decaffeinated (Aeschbacher and WUrzner, 1980; Aeschbacher e al. , 1980;
Nagao et^ al* , 1979). Although caffeine has been reported to be muta-
genic to bacteria (Clarke and Wade, 1975; Demerec et al . , 1948, 1951;
Gezelius and Fries, 1952; Glass and Novick, 1959; Johnson and Bach,
1965; Kubitschek and Bendigkeit, 1958, 1964; Novick, 1956), it could
not have been responsible for the mutagenicity of coffee observed in
these reports, since decaffeinated coffee was as mutagenic as regular
coffee and caffeine itself was not detected as a mutagen under the test
conditions used (Aeschbacher t ad. , 1980; Nagao et_ al. , 1979). Studies
examining the possible carcinogenicity of coffee are discussed in Chap-
ter 12.
Black tea, green tea, and roasted tea were mutagenic to S^. typhi-
murium strain TA100 in the absence of added enzymes (Nagao et al.,
1979). When extracts of Aspergillus niger or human feces containing
enzymes capable of hydrolyzing glycosides were added, tea became muta-
genic to . typhimurium strain TA98 (Nagao e al . , 1979; Tamura et al. ,
1980). Acid hydrolysis of green or black tea also caused mutagenic
13-12
activity to be released (Uyeta et^ a.1. , 1981). The flavonols quercetin,
kaempferol, and myricetin have recently been shown to account for most
of the mutagenic activity of an acid hydrolysate of green tea (Uyeta et
al. , 1981). Grape juice was also found to be mutagenic to strain TA98,
although only when tested with fecal extracts containing glycosidases
(Tamura e al* , 1980) .
Mutagenic activity has also been detected in concentrates of 17 out
of 27 commonly consumed Chinese alcohoJJLc beverages, mostly fermented
from rice, glutinous rice, and barley (Lee and Fong, 1979). The muta-
genic spirits were those that had been distilled only once or to which
herbs or meat had been added. Evaporated residues from 12 out of 13
Japanese, Scotch, and North American whiskies were found to contain
mutagenic activity (Nagao et^ aJN , 1981). This activity did not require
the addition of glycosidases or mammalian enzymes. It was mutagenic to
jS_. typhimurium strain TA100, but not to TA98, indicating that it was
inducing base-pair substitution rather than frameshift mutations. Some
French brandies and apple brandies were also mutagenic when concentrated
or fractionated (Loquet et al. , 1981; Nagao et al. , 1981).
Extracts of relatively few fruits, vegetables, and beverages are
mutagenic. When Stoltz .! (in press, a,b) fractionated extracts
of 28 beverages and 40 fruits and vegetables, only 3 beverages and 5
fruits and vegetables showed reproducible mutagenic activity. The
activity of three of the fruits (strawberries, raspberries, and peaches)
was due to residues of the fungicide captan. Quercetin accounted for
the mutagenicity of the remaining fruit and vegetable (raisins and
onions) as well as two of the beverages (red wine and grape juice). The
mutagen in coffee was not Identified. This extensive survey of frac-
tionated extracts of 68 foods did not reveal the presence of any muta-
genic chemicals or foods that had not been previously reported. Simi-
larly, Bjeldanes et^ suL. (in press, a,b) found no significant mutagenic
activity in extracts of eggs, milk, cheese, or tofu unless they had been
cooked at high temperatures or to the point of darkening. Thus, with
the exception of mutagens produced by cooking, it seems unlikely that
large numbers of mutagens remain to be discovered in common foods.
MODIFIERS OF MUTAGENIC ACTIVITY
A number of substances in food have been reported either to enhance
or to diminish the mutagenic activity of other substances. Most of
these effects have been observed in in. vitro test systems, and their
relevance to effects in intact mammals is unknown. Modifiers of muta-
genicity can be either comutagens or antimutagens. A comutagen is a
substance that enhances the mutagenic activity of a chemical although
it is not in itself mutagenic. This enhancement may take one of two
forms: it may strengthen the mutagenic response of chemicals that are
themselves mutagenic or may create a mutagenic response from nonmutagens.
Similarly, an antimutagen is a substance that reduces or eliminates the
mutagenic activity of a mutagen.
13-13
Barman and Norharman
Among the more interesting comutagens discovered in recent years are
barman (l-methyl-3*~carboline) and norharman (g-carboline) . Norharman is
present in tobacco tar (Poindexter and Carpenter, 1962) as well as in
toasted bread, broiled beef, and broiled sardines (Yasuda et_ al. , 1978).
Harman is found in these same sources as well as in mushrooms and in
Japanese sake (Takase and Murakami, 1966; Takeuchi et al., 1973).
These compounds were identified as comutagens when fractionation of
pyrolyzed tryptophan resulted in a significant loss of mutagenic activity
on . typhimurium. Mixing the fraction containing barman and norharman
with the fraction containing Trp-P-1 and Trp-P-2 restored the mutagenic
activity of these mutagens (Nagao e^t auL. , 1977d). Norharman, which is
at most marginally mutagenic, has been shown to be comutagenic when
mixed with a variety of chemicals, including 4-dimethylaminoazobenzene,
(Nagao e a_l . , 1977d), aniline, -toluidine (but not m- or -toluidine)
(Nagao e l. , 1977e), nitrosodiphenylamine (Wakabayashi t 1. , 1981),
3-aminopyridine, 2~amino-3-methylpyridine (Sugimura ejt_ i/ 1982),
2-acetylaminof luorene, 2 -aminof luorene, and N~hydroxy-2-acetylamino-
fluorene (Umezawa e al. , 1978). These chemicals all require an in.
vitro mammalian metabolic activation system for mutagenic activity. In
addition, norharman is comutagenic with Itf-acetoxy- 2-acetylaminof luorene
in the absence of any metabolic activation system (Umezawa jil- > 1978).
Aniline, which is nonmutagenic in the absence of norharman, was
believed for many years to be noncarcinogenic. Its weak carcinogenic
activity has only recently been demonstrated (National Cancer Institute,
1978). Although the mutagenic activity of a number of chemical carcino-
gens can only be observed in the presence of norharman, data are insuffi-
cient to justify recommending the inclusion of norharman in routine
screening. The possibility that many "false positive" results might be
obtained with norharman has not yet been ruled out.
The mechanism of the comutagenic action of barman and norharman is
still unclear. Although these comutagens are generally believed to
exert their activity by affecting the metabolic activation of the test
compounds, they may act through other mechanisms as well. For example,
the mutagenicity of N-acetoxy- 2-acetylaminof luorene, which does not
require activation, was enhanced by the addition of harman and/ or nor-
harman (Umezawa et_ a^L. , 1978).
A number of substances in foods can reduce the activity of certain
mutagens in in vitro test systems. For example, Morita et_ al^. (1978)
reported that juices prepared from some common vegetables, fruits, and
spices, including cabbage, broccoli, green pepper, eggplant, apple,
shallot, ginger, pineapple, and mint leaf, reduced the mutagenic acti-
vity of tryptophan pyrolysates. Lai (1979) and Lai e al . (1980) have
also found antimutagenic activity in extracts of wheat sprouts, leaf
13-14
lettuce, parsley, brussels sprout s, mustard greens , spinach, cabbage,
broccoli, and other vegetables. Although they concluded that the antt-
mutagenic substance in these vegetables is chlorophyll, certain food
substances without chlorophyll, such as apples, also inhibit mutagenic
activity (Morita eit al. , 1978), indicating that some factor in foods
other than chlorophyll can be antimutagenic.
Heroin
Certain pigments derived from animal systems have also been re-
ported to have antimutagenic activity* For example, hemin inhibited
the activity of a number of polycyclic mutagens including benzo[ajpy-
rene, 3-methylcholanthrene, 2-acetylaminofluorene, 2-nitrofluorene, and
alfatoxin B^ as well as several mutagenic amino acid pyrolysates, such
as Trp-P-1 and Trp-P-2 (Arimoto t_a]U , 1980a,b). The heme metabolites
biliverdin and bilirubin also interfered with the mutagenic activity of
some of these compounds. The mechanism of these antimutagenic effects
awaits complete elucidation. Hemin interfered with the mutagenic activ-
ity of 2-nitrofluorene and the activated forms of Trp-P-1 and Glu-P-1,
all of which are mutagenic to S^. typhimurium in the absence of a mammal-
ian metabolic activation system. Therefore, at least some of the
mutagenic activity of hemin must be unrelated to such activation.
Fatty Acids
Other chemicals in foods have also been reported to inhibit muta-
genic activity. For example, the unsaturated fatty acids oleic acid
and linoleic acid (but not the saturated fatty acids stearic acid and
palmitic acid) inhibited the mutagenic activity of a number of chemicals
for S. typhimurium (Hayatsu et al . , 1981a,b). The mechanism for this
inhibition is unknown.
Nitrite
Yoshida and Matsumoto (1978) reported that when pyrolyzed casein
(a mutagenic extract of roasted chicken meat), tobacco-smoke condensate,
and certain aromatic amines were treated with nitrite under acidic con-
ditions, there was a decrease in the mutagenic activity of these sub-
stances when tested on Salmonella typhimurium. Concentrations of sodium
nitrite as low as 3 ing/liter were sufficient to cause a loss of most of
Moanf * gei ^ C activit y of casel * pyrolysate. Similarly, Tsuda et al.
(1980) found that acidic treatment with 2.3 ing/liter solution oF~s^dium
nitrite resulted in the loss of mutagenic activity of Trp-P-1, Trp-P-2,
and Glu-P-1.
A more complex situation has been found to exist for the interaction
ot nitrite with 2-amino-a-carboline (Tsuda e al. , 1981). At pH of
13-15
approximately 4, the reaction results in a loss of mutagenic activity
through the conversion of 2-amino~ct-carboline to the nonmutagen
2-hydroxy~a-carboline. However, when the pH was below 3*5, a new,
direct-acting mutagen was formed: 2-hydroxy-3~nitroso-a~carboline
Thus, nitrite can either neutralize mutagens or result in the forma-
tion of new mutagens* The ability of nitrite to interact with dietary
amines to form mutagenic and carcinogenic N-nitrosamines is discussed
in Chapter 12.
Antioxidants
A number of antioxidants have been shown to inhibit the mutagenicity
of a variety of chemicals. For example, McKee and Tometsko (1979) found
that butylated hydroxyanisole (BHA) and butylated hydroxy toluene (BHT)
were antimutagenic In the presence of a series of mutagens that require
in vitro metabolic activation, but not in the presence of mutagens that
are directly mutagenic to S_. typhimurlum without an added metabolic
activation system* Similarly, Katoh ejt^ aJL. (1980) found that BHA in-
hibits the mutagenicity of benzo[a.]pyrene in Chinese hamster V-79 cells,
but not the mutagenicity of the direct-acting compound N-acetoxy-2-ace-
tylaminofluorene. These findings are consistent with the hypothesis
that these antioxidants interfere with the In vitro metabolic activa-
tion of the mutagens, rather than reacting with them or their active
metabolites directly. Further evidence that a metabolism-modifying
mechanism is related to the ability of certain chemicals to exert
anticarcinogenic activity is discussed in Chapter 15.
The observation that some antioxidant antimutagens appear to act by
interfering with metabolic activation does not exclude the possibility
that, In some cases, direct reaction with a mutagen may be an Important
mechanism pf action. For example, Shamberger et al. (1979) have found
that BHT, ascorbic acid, vitamin E, and selenium can Interfere with the
mutagenicity of g-propiolactone and. In some strains of IS. typhimurlum,
malonaldehyde . These two chemicals do not require a mammalian-derived
metabolic activation system for activity. Similarly, Guttenplan (1978)
attributes the ability of ascorbic acid to Inhibit the mutagenic activity
of the direct-acting mutagen N-methyl-NT-nltro-N-nitrosoguanidine (MNNG)
to a direct reaction between ascorbate and the mutagen.
Rosin and Stlch (1979) reported that some antioxidants, including
sodium bisulfite and sodium ascorbate, Inhibit the mutagenicity of MNNG
in $_. typhimurlum, but not that of another direct-acting mutagen,
N~acetoxy~2-acetylaminofluorene. Other antioxidants tested inhibited
both or neither of these mutagens. These findings probably reflect an
underlying complex mechanism concerning the inhibition by antioxidants
of the mutagenicity of even direct-acting mutagens.
Retlnol (vitamin A alcohol) Inhibits the mutagenic activity of
2-aminofluorene and aflatoxin Bj, both of which require metabolic
13-16
activation, but not that of the direct-acting mutagens adriamycin
and diepoxybutane (Baird and Birnbaum, 1979; Busk and Ahlborg, 1980).
Similar to the antioxidants discussed above, these results may indicate
that retinol inhibits mutagenesis by interfering with metabolic acti-
vation rather than by acting as a scavenger of mutagenic chemicals.
However, more experimental evidence is needed to clarify this point'.
SUMMARY AND CONCLUSIONS
Considerable attention has recently been directed toward the pre-
sence of mutagenic activity in foods. Many vegetables contain muta-
genic flavonoids such as quercetin, kaempferol, and their glycosides.
Furthermore, some substances found in foods can enhance or inhibit the
mutagenic activity of other compounds. Mutagens in charred meat and
fish are produced during the pyrolysis of proteins that occurs when
foods are cooked at very high temperatures. Normal cooking of meat at
lower temperatures can also result in the production of mutagens.
Smoking of foods as well as charcoal broiling results in the deposition
of mutagenic and carcinogenic polynuclear aromatic compounds such as
benzo[ajpyrene on the surface of the food.
The production of mutations in bacterial or other tests is an
indication that a chemical may be carcinogenic in animals. However,
many mutagens detected in foods have not been adequately tested for
carcinogenicity. Of those that have been tested, the data on the
carcinogenicity of the mutagenic flavonol quercetin are conflicting,
and several mutagens isolated from pyrolyzed proteins or amino acids
appear to be carcinogenic. It is not yet clear to what extent the
mutagens produced by pyrolyzing proteins or amino acids are found in
normally cooked foods. The finding that some constituents of food can
enhance or inhibit the in vitro mutagenicity of other compounds should
not be interpreted as meaning that these compounds would produce the
same effects in living animals or humans.
If mutagens that are widely distributed in common foods are con-
sistently found to cause cancer in animals, many factors should be
considered before action is taken to reduce exposure. For example,
cooking of meat and fish produces mutagens, but it also destroys
pathogenic microorganisms and parasites. Furthermore, some foods con-
tain mutagenic flavonoids but also have high nutritional value.
13-17
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13-22
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13-23
Nagao , Mo, Y. Takahashi, K. Wakabayashi, and T* Sugimura. 1981.
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13-24
Simmon, V. F. 1979. In vitro mutagenicity assays of chemical carcino-
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13-25
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13-26
Tsuda, M. , M. Nagao, T. Hirayama, and T. Sugimura* 1981* Nitrite con-
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Presence of 3-amino-l,4-dimethyl-5H-pyrido[4 ,3Hb]indole in
beef. Gann 71:745-746.
13-27
Yamaguchi, K. , K. Shudo, T Okamoto , T. Sugimura, and T. Kosuge. 1980b.
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Trp-P-2, in broiled fish. Cancer Lett. 9:75-83.
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1978. Isolation and structure determination of mutagenic substances in
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Yasuda, T. , Z. Yamaizumi, S. Nishimura, M. Nagao, Y. Takahashi, H. Fujiki,
T. Sugimura, and K. Tsuji. 1978. Detection of comutagenic compounds,
barman and norharman in pyrolysis product of proteins and food by gas
chromatograpb-mass spectrometry. Nippon Can Gakkai Sokai Kiji 37:6).
Abstract 41.
Yosbida, D., and T. Matsumoto. 1978. Changes in mutagenicity of protein
pyrolyzates by reaction with nitrite. Mutat. Res. 58:35-40.
Yoshida, D., and H. Okamoto. 1980. Formation of mutagens by heating
the aqueous solution of amino acids and some nitrogenous compounds
with addition of glucose. Agric. Biol. Chem. 44:2521-2522.
Yoshida, D., T. Matsumoto, R. Yoshimura, and T. Matsuzaki. 1978. Muta-
genicity of amino-a-carbolines In pyrolysis products of soybean
globulin. Biochem. Biophys. Res. Commun. 83:915-920.
CHAPTER 14
ADDITIVES AND CONTAMINANTS
ADDITIVES
This section contains summaries of data on a few selected compounds
that are added directly to foods, as well as for processing aids and
some compounds that may migrate into foods in small amounts as a result
of their use in packaging.
Saccharin
Saccharin has been used as a nonnutritive sweetener since 1907.
In 1977, an estimated 2.2 million kilograms of saccharin and sodium
saccharin were produced in the United States and an additional 1.3
million kilograms were imported (National Academy of Sciences, 1978).
During that year, approximately 2.9 million kilograms (^83% of the
domestic and imported saccharin) were used in foods (U.S. Department
of Agriculture, 1978).
Epidemiological Studies. The use of nonnutritive sweeteners
has been studied primarily to determine their relationship to bladder
cancer. Results from studies of diabetics did not indicate that there
is a direct association between saccharin use and bladder cancer
(Armstrong and Doll, 1975; Armstrong e al . , 1976; Kessler, 1970);
however, diabetics are not generally representative of the general
population in epidemiological studies of cancer incidence and mor-
tality since they differ in several important respects. For example,
diabetics as a group smoke less, and since smoking is associated with
bladder cancer, less cancer at that site might be anticipated among
these subjects (Armstrong and Doll, 1975; Christiansen, 1978).
Burbank and Fraumeni (1970) found no increase in mortality from
bladder cancer in the United States following the widespread intro-
duction of nonnutritive sweeteners. They examined mortality rates for
this cancer after saccharin was introduced early in this century and
after a 10:1 mixture of cyclamate : saccharin came into use during 1962.
In England and Wales a cohort analysis of bladder cancer mortality from
1911 to 1970 provided no evidence of any disruption of mortality trends
for either men or women corresponding to the introduction of saccharin
(Armstrong and Doll, 1974). However, time-trend studies generally
cannot detect weak effects and can detect no effects for diseases with
long latency periods, if only a short time has elapsed between exposure
to the substances and the observation.
The consumption of saccharin by bladder cancer patients and healthy
controls has been compared in several case-control studies, although
14-2
most of these studies were not originally designed to investigate the
relationship between nonnutrltive sweeteners and bladder cancer.
In a case-control study based on responses to questionnaires from 74
female cases, 158 male cases, and an equal number of matched controls,
Morgan and Jain (1974) observed that prolonged use of any nonnutritive
sweetener was not associated with an increased risk in males and was
associated with a reduced risk for females* In another study based on
mailed questionnaires, Simon e_t_ ad. (1975) studied women only, and
found no differences between the cases and controls in either saccharin
or cyclamate use.
Howe et al. (1977) conducted a case-control study of 480 male and
152 female sex-matched pairs* They observed that men who used nonnu-
tritive sweeteners had a 60% increase in risk of bladder cancer and
provided evidence of a dose-response relationship. On the other hand,
there was no significant increase in risk for women. These preliminary
findings were confirmed in a later study by the same investigators, who
reanalyzed the data, controlling for potential confounding factors such
as smoking and using a logistic regression model (Howe !/ 1980).
In a case-control study of 519 bladder cancer patients and twice
as many controls, Kessler and Clark (1978) found no evidence of a link
between nonnutrltive sweetener consumption and bladder cancer. Miller
et_ al. (1978) studied 265 bladder cancer patients and 530 matched con-
trols. They also found no significant risk associated with the regular
use of nonnutritive sweeteners. Morrison (1979) found no association
between current use of nonnutritive sweeteners and bladder cancer in 13
cases and 10,874 controls.
Morrison and Buring (1980) evaluated the relationship between cancer
of the lower urinary tract and the consumption of nonnutritive
sweeteners in a case-control study of 592 patients and 596 controls.
Overall, there was no increase in risk for- lower urinary tract cancer
among users of nonnutritive sweeteners. However, in a subgroup of
nonsmoking women, there were elevated risks of 2.1 for use of sugar
substitutes and 2*6 for use of dietetic beverages.
Wynder and Stellman (1980) conducted a case-control study of 302
men and 65 women with bladder cancer and an equal number of matched
controls. They also found no association between bladder cancer and
the consumption of nonnutritive sweeteners or dietetic beverages.
The National Cancer Institute (NCI) and the Food and Drug Adminis-
tration (FDA) jointly sponsored a large scale case-control study in
which 3,010 bladder cancer patients and 5,783 population controls were
interviewed. This investigation was designed specifically to evaluate
the relationship between nonnutritive sweetener consumption and bladder
cancer. Subjects who reported ever having used nonnutritive sweeteners
or artifically sweetened foods or beverages were found to have no in-
crease in the risk of bladder cancer. However, white nonsmoking women
14-3
who had not been exposed to known bladder carcinogens such as azo dyes
were found to have an increased risk of bladder cancer with increased
nonnutritive sweetener consumption (relative risk of 2*7-3.0 in heavy
users for at least 10 years and a suggested dose-response relationship).
Users of both tabletop sweeteners and diet drinks, with a heavy use of
at least one of the two, showed a relative risk of 1.5 (Hoover and
Strasser, 1980).
The International Agency for Research on Cancer (1980) concluded,
"Although a small increase in the risk of urinary bladder cancer in the
general population or a larger increase in some individuals consuming
very high doses of saccharin cannot be excluded, the epidemiological
data provide no clear evidence that saccharin alone, or in combination
with cyclamates, causes urinary bladder cancer."
There have also been some observations concerning consumption of
saccharin and cancer at other sites, for example, pancreatic cancer.
An increase in deaths from pancreatic cancer was found in cohort
studies of diabetics (Armstrong e al. , 1976; Kessler, 1970). Blot et_
al. (1978) found a direct correlation of pancreatic cancer mortality by
county in the United States with diabetes mellitus in women, but not in
men, who consumed saccharin. In a case-control study, Wynder et ajl.
(1973) found a direct association of pancreatic cancer with early-onset
diabetes in women who used saccharin.
Experimental Evidence; Carcinogenicity . The carcinogenicity of
saccharin has been reviewed extensively (National Academy of Sciences,
1978). The following discussion focuses on some recent data.
There was no evidence of saccharin-induced carcinogenesis in a
number of single-generation studies in which various doses of saccharin
were fed to several strains of mice and rats (Furuya et al. , 1975;
Homburger, 1978; National Institute of Hygienic Sciences, 1973; Roe est
al. , 1970; SchmShl, 1973) and to hamsters and rhesus monkeys (Althoff
et.a.1. , 1975; McChesney et al. , 1977).
In a single-generation study, Wistar specific-pathogen-free (SPF)
rats were fed saccharin at either 4 g/kg body weight (bw) daily in the
diet for 2 years or saccharin containing 698 mg/kg o-toluenesulfonamide
(OTS) at 2 g/kg bw in drinking water daily for the same period. The
treated males in both groups developed more tumors than did the
untreated controls, but there was no significant difference in the
females (Chowaniec and Hicks, 1979).
In another single-generation study, Charles River CD rats fed 5%
sodium saccharin (free of OTS) for their lifetime had a higher inci-
dence of benign and malignant bladder tumors than observed in the
untreated controls (D. L. Arnold e al . , 1977, 1980).
Saccharin has also been tested In two-generation carcinogenicity
bioassays in which parent animals (the FQ generation) are fed
14-4
saccharin from weaning through pregnancy until their offspring are
weaned. The offspring (F^ generation), already exposed to saccharin
in utero , are given the same diet as their parents for the rest of
their lives.
In one such study, there was no difference in the incidence of
tumors in treated or control Swiss SPF mice in either generation
(Kroes et_ jut. , 1977). In three two-generation studies with Charles
River and Sprague-Dawley rats (D. L. Arnold et_ al. , 1977, 1980; Taylor
and Friedman, 1974; Tisdel et al* , 1974; U.S. Department of Health, Edu-
cation, and Welfare, 197 3a, 7, the incidence of bladder tumors In
treated male rats of the F^ generations given the highest dose was
significantly higher than that in controls in all three studies and
in the F males in one study (D. L. Arnold e al . , 1977, 1980).
Saccharin (2 or 4 g/ kg bw/day in diet) increased the incidence of
and decreased the latent period for tumor development in animals
treated with N-nitroso-N-methylurea (NMU) (Chowaniec and Hicks, 1979;
Hicks et^ al. , 1978) or with N~[4(5-nitro-2-furyl)-2-thiazolyl]forma-
mide (FANFT) (Cohen t al.. , 1979). In several in vitro cell culture
systems, saccharin also exhibited an activity similar to the tumor-
promoting activity of tetradecanoylphorbol acetate (Trosko et al.,
1980).
Experimental Evidence: Mutagenlcity, Efforts to test saccharin for
mutagenicity have produced conflicting results. In the Ames Salmonella
reverse mutation assay, saccharin of various degrees of purity was not
mutagenic (Ashby et_ al. , 1978; McCann, 1977; Poncelot et^ al . , 1979).
Batzinger et al. (1977) reported that saccharin was weakly mutagenic to
*L* typhimurium TA98 and TA100 strains In a modified plate assay and
that the urine of animals fed saccharin contained mutagens for TA98 and
TA100 strains.
Weak mutagenic effects were observed in the mouse lymphoma assay
(Clive et^ al. , 1979). Dominant lethal mutations were found In animals
fed 1.72% sodium saccharin in the diet (Rao and Qureshi, 1972), and a
dose-dependent increase in unscheduled DNA synthesis in fibroblasts
from humans was reported by Ochi and Tonomura (1978).
Continuous exposure to saccharin following treatment of C3H/10T1/2
cells with 3-methylcholanthrene led to a significant increase in the
number of transformed colonies (Mondal et_ aJL . , 1978). Saccharin also
induces chromosome aberrations in mammalian cells (Abe and Sasaki, 1977;
McCann, 1977; Yoshida et_ a_l. , 1978) and sister chromatid exchanges
in cells from humans (Wolff and Rodin, 1978).
Summary and Conclusions. The epidemiological data do not provide
a clear indication of an association between the use of nonnutritive
sweeteners and cancer, and the results of most studies of bladder can-
cer have shown no association. Exceptions are the study by Howe et al.
(1977), which showed a direct association in men, and those by Hoover"""
14-5
and Strasser (1980) and Morrison and Buring (1980), whose results
suggested a possible effect in certain subgroups. Since the data
regarding saccharin and pancreatic cancer are based on studies of
diabetics, who as a group are not representative of the general
population, no firm conclusions can be drawn.
Experimental studies have provided sufficient evidence that
saccharin alone, given at high doses, produces tumors of the urinary
tract in male rats and can promote the action of known carcinogens in
the bladder of rats* There is limited evidence of its carcinogenicity
in mice.
Cyclamates
Until 1970, when cyclamates were banned from use in the United
States (U.S. Food and Drug Administration, 1970), cyclamic acid, sodium
cyclamate, and calcium cyclamate were used as nonnutritive sweeteners
in carbonated beverages, in dry beverage bases, in diet foods, and in
sweetener formulations. Sodium and calcium cyclamates were used pri-
marily as a 10:1 cyclamate: saccharin salt mixture (Wiegand, 1978).
Epidemiological Evidence* Epidemiological data on cyclamates alone
are not adequate, because cyclamates were rarely used without
saccharin. Thus, it was not usually possible to distinguish the
consumption of cyclamate-containing mixtures from the consumption of
saccharin.
Experimental Evidence; Carcinogenicity. Swiss and Charles River
CD mice receiving up to 5% sodium cyclamate for 18 months or 24 months,
respectively, did not yield evidence that cyclamates are carcinogenic
(Homburger, 1978; Roe e al. , 1970). When sodium cyclamate (99.5%
pure) was administered in drinking water (6 g/liter, or 20-25 mg/mouse)
to mice for their lifetime, there was no evidence of carcinogenesis in
male and female C3H mice, but there was an increased incidence of lung
tumors in RIII male and XVII female mice and of hepatocellular car-
cinomas in (C3H x RIlI)Fi male mice (Rudali t al . , 1969). Female
SPF mice fed diets containing up to 7% sodium cyclamate for 80 weeks
had a higher, but statistically insignificant increase in the incidence
of lymphosarcomas than did the controls (Brantom et^ al. , 1973).
Osborne Mendel rats fed sodium cyclamate at 0.4%, 2%, or 10% in
their diet for 101 weeks had an increased incidence of transitional
cell papillomas of the urinary bladder, although the number of animals
examined histopathologically was small (Friedman e ail. , 1972). Cycla-
mate (1.0 g/kg bw/day) fed for 2 years led to a slight increase in
the incidence of bladder tumors in Sprague-Dawley rats (Hicks and
Chowaniec, 1977; Hicks et al. , 1978).
Lifetime studies in one generation of Syrian golden hamsters
(Althoff et^a^., 1975) and rhesus monkeys (Coulston et. al. , 1977) and
14-6
a six-generation study of Swiss SPF mice (Kroes et_ SL!. , 1977) produced
no evidence that sodium cyclamate is carcinogenic*
Female Wistar SPF rats treated with 1*5 mg NMU and subsequently
fed sodium cyclamate (containing 13 mg/kg cyclohexylamine) in diets at
doses of 1, 1.5, or 2.0 g/kg bw/day for their lifetime or up to 2 years
had a significantly higher incidence of bladder cancer and a signifi-
cant decrease in latent period (8 weeks vs. 87 weeks) compared to
animals treated with NMU only and the untreated controls (Hicks et al.,
1978).
In another study, a single 2 .fag dose of NMU was instilled into the
urinary bladder of female Wistar rats before giving them a diet con-
taining sodium cyclamate at 2% for 10 weeks and then at 4% for the rest
of their lives. The overall incidence of urinary tract tumors was 70%
in those given NMU and sodium cyclamate, 57% in animals receiving NMU
alone, and 65% in another control group given NMU and calcium carbonate
(Mohr ejt l. > 1978).
Wistar weanling rats were fed a 10:1 mixture of sodium cyclamate:
saccharin in the diet at doses of 0, 500, 1,120, or 2,500 mg/kg bw/day
for 2 years. After the 79th week, 50% of the survivors from all three
treated groups were also fed cyclohexylamine hydrochloride, in addition
to the cyclamate : saccharin diet. The animals consuming the diet con-
taining the highest levels of cyclamate rsaccharin (with and without
added cyclohexylamine hydrochloride) were found to have a significantly
higher number of urinary bladder cancers (9/25 males and 3/35 females)
compared to the controls (0/35 males and 0/45 females). Of the tumor-
bearing animals, three males and two females had received cyclohexyl-
amine, indicating that cyclohexylamine hydrochloride Is not carcinogenic
(Oser et^ al. , 1975).
Experimental Evidence; Mutagenicity. There are no published
data on the ability of cyclamates alone to induce point mutations in
microbial and mammalian cells. In two studies, cyclamates induced
chromosome breaks in leukocytes from humans (Ebenezer and Sadaslvan,
1970; Tokumitsu, 1971).
No increase in chromosome aberrations was observed in hamsters
given oral doses of sodium cyclamate or cyclohexylamine sulfate
(Machemer and Lorke, 1976).
Summary and Conclusions. There are no adequate epidemiological
data on the effect of cyclamate alone since it was rarely consumed by
humans in the absence of saccharin.
The experimental data provide limited evidence for the carcinogenic-
ity of cyclamates in mice and rats. In addition, there is evidence
that cyclamates can promote the action of known carcinogens in the
bladder.
14-7
Aspartame
Aspartame, the methyl ester of the amino acids phenylalanine and
aspartlc acid, is approximately 180 times sweeter than sugar (Mazur,
1976). In July 1981 the FDA approved its use as a sweetener or
flavoring agent in certain foods (U.S. Food and Drug Administration,
1981) Aspartame cannot be used in soft drinks because of its
instability in liquids during storage.
Epidemiological Evidence . Since aspartame has been on the market
only since 1981 and in only a few countries (e.g., Belgium, France, and
Canada), there are no epidemiological data regarding its association
with cancer in humans.
Experimental Evidence : Carcinogenicity . A number of feeding
studies have been conducted on mice and rats under the sponsorship
of the G. D. Searle Co. to test the carcinogenicity of aspartame. In
one of these studies, male' and female Charles River mice received
aspartame at (control), 1.0, 2.0, or 4.0 g/kg bw/day in their diet
for 2 years. No tumors attributable to aspartame ingestion were
reported (G. D. Searle and Co., 1974a). In another study, no statis-
tically significant differences in the incidence of neoplasms were
observed in the urinary bladders of control and treated mice 26 weeks
after implantation of cholesterol pellets containing aspartame or its
breakdown product diketopiperazine (DKP) (G. D. Searle and Co., 1973a).
Male and female Sprague-Dawley rats fed aspartame in the diet at
various levels for up to 2 years were observed for the incidence of
brain tumors (G. D. Searle and Co., 197 3b). After the study was com-
pleted, the FDA appointed an independent board of inquiry to review
the data. The board concluded that aspartame was a possible carcino-
gen, based on three of the study's findings: The incidence of brain
neoplasms in aspartame-fed rats was greater than that in controls, a
possible dose response was observed when tumor incidence in the con-
trols was compared with the two lower dose and the two higher dose
treatment groups combined, and there was a decrease in the latent
period for gliomas (U.S. Food and Drug Administration, 1980a).
Investigators at the G. D. Searle Co. interpreted these data
differently. They contended that statistical analysis using con-
current instead of historical controls indicates that there was no
significant increase in tumor incidence, that more appropriate sta-
tistical tests show no dose response, and that the board of inquiry
made errors concerning the time of death of certain rats (U.S. Food
and Drug Administration, 1980a).
In a follow-up study by the Searle group, rats were exposed in
utero to aspartame at (control), 2, and 4 g/kg bw and maintained on
this diet for the duration of their lives (G. D. Searle and Co., 1974b)<
14-8
The incidence of brain tumors was: 4/115 (3.4%), 3/75 (4.0%), and 1/80
(1.3%), respectively, which indicated no statistically significant
difference between the control and treated groups.
Recently, Ishii et_ al. (1981) also found no evidence for carcino-
genicity in chronic feeding studies with Wistar rats given aspartame or
a mixture of aspartame and DKP. The FDA concluded that this study
provides additional evidence favoring the safety of aspartame (U.S.
Food and Drug Administration, 1981).
Groups of five male and female beagle dogs were fed aspartame at
(control), 1.0, 2.0, and 4.0 g/kg bw in their diet for more than 106
weeks. No evidence of neoplasia was observed in any of the treated or
control groups (G. D. Searle and Co., 1973c).
Experimental Evidence; Mutagenicity. Aspartame and DKP were
negative in the Ames test with and without using the S9 fraction from
rats (G. D. Searle and Co., 1978a,b,c). Similarly, no evidence of the
mutagenicity of these compounds was observed in the host-mediated assay
in rats and mice at doses ranging from 0.25 to 8.0 g/kg/ day (G. D.
Searle and Co., 1972a,b, 1974c). Aspartame and DKP (1 or 2 g/kg
bw/day) were also negative in the in vivo dominant lethal assay in rats
(G. D. Searle and Co., 1973d).
Summary and Conclusions. Aspartame has been used as a sweetener
in Belgium and France only since 1981. It has recently been approved
for use in Canada and the United States. Consequently, there are no
epidemiological data pertaining to its effects on human health.
Aspartame appears to be negative in jLn vitro bacterial mutagenic-
ity tests, in the host-mediated assay, and in dominant lethal tests
in rats. It has been reported to be noncarcinogenic in chronic feeding
studies in mice and dogs, most of which were conducted by G. D. Searle
and Company. Although a board of inquiry appointed by the FDA con-
cluded that aspartame may be neurooncogenic in rats, additional evi-
dence led the FDA to conclude that aspartame is not carcinogenic in
animals.
Butylated Hydroxy toluene (BET) and Butylated Hydroxyanisole (BHA)
Butylated hydroxytoluene (BHT) and butylated hydroxyanisole (BHA)
are widely used as food additives, mainly because of their preservative
and antioxidant properties. These compounds are included in the FDA's
list of substances generally recognized as safe (GRAS). Many studies
have been conducted to test them for acute and chronic toxicity under a
variety of experimental conditions, ranging from in vitro studies to in
vivo studies in animals (U.S. Food and Drug Administration, 1977a).
Based on the evidence from these studies, the FDA in 1977 recommended
that BHT be removed from the GRAS list and proposed interim regulations
pending future studies.
14-9
Epidemiological Evidence* There are no epidemiological studies
concerning the effects of BHT and BHA on human health.
Experimental Evidence for BHT: Carcinogenicity* Male and female
B6C3FJL mice were fed 0, 0.3%, or 0.6% BHT in the diet for 107 to 108
weeks. In female mice receiving the low dose, the incidence of alveo-
lar/bronchiolar adenomas or carcinomas was significantly higher than
in the controls, but there was no dose response (National Cancer
Institute, 1979a). In a similar study of male and female Fischer 344
rats, the incidence of tumors in treated animals was not statisically
different from that in controls (National Cancer Institute, 1979a) .
Experimental Evidence for BHT; Promoting Effects. Three groups of
A/J mice were injected with urethan, 3-methylcholanthrene, or nitrosodi-
methylamine and then given repeated injections of BHT. The treatment
with BHT significantly increased the multiplicity of lung tumors induced
by all three carcinogens (Witschi et_ ajL. , 1981).
BHT administered orally increased the incidence of lung tumors in
A/J mice pretreated with a single dose of urethan (Witschi, 1981).
When injections were begun as late as 5 months after the urethan was
administered, they still produced an increase in the incidence of lung
tumors. BHT does not appear to enhance lung tumor formation, even if
given repeatedly prior to urethan administration. This suggests that
BHT may be a tumor promoter (Witschi, 1981; Witschi et al., 1977). BHT
also appears to have some promoting activity in BALBTc" mice (Clapp et
al. , 1974) and in male Sprague-Dawley rats treated with 2-aminoacetyl-
fluorene (2-AAF) (Peraino et^ al. , 1977).
Experimental Evidence for BHT: Mutagenicity. BHT inhibited
cell-to-cell communication of mammalian cells in vitro an indication
of promoting activity (Trosko al_. , 1982). When BHT in concen-
trations of 0-50 yg/ml were added to phytohemagglutinin-stimulated
cultures of leukocytes from humans, it resulted in a dose-dependent
decrease in cell survival, as well as in an uncoiling of the chromo-
somes (Sciorra !/, 1974). In the sister chromatid exchange assay,
BHT was negativ~and it did not induce chromosome aberrations (Abe and
Sasaki, 1977).
Experimental Evidence for BHA: Carcinogenicity. The administra-
tion of BHA had no significant effect on the tumor yield or tumor
multiplicity in Swiss Webster mice injected with urethan and then given
BHA in the diet (Witschi, 1981). In other experiments, repeated intra-
peritoneal injections of BHA at high doses produced a slight, although
not statistically significant, increase in lung tumors in male A/J mice
(Witschi e al_. , 1981). Under different experimental conditions, BHA
has been shown to inhibit the activity of a wide variety of carcinogens
(see Chapter 15) .
Experimental Evidence for BHA; Mutagenicity. BHA was positive in
the sister chromatid exchange assay with Chinese hamster cells as in-
dicator organisms; however, it did not induce chromosome aberrations in
these cells (Abe and Sasaki, 1977).
14-10
Summary and Conclusions* BHT and BHA are used as antioxidants and
preservatives in many types of foods* There are no epidemiological
studies concerning their effect on human health*
At least one adequate bioassay to test the carcinogenicity of
BHT has been conducted in each of two specie s, the mouse and the
rat, without clear evidence of carcinogenicity under the conditions
of the tests* Evidence for the enhancement of tumorigenesis by BHT
is restricted to two experimental systems carcinogen-induced lung
tumors in mice and liver tumors in rats. The studies in mice have
been repeated several times with other carcinogenic initiators*
These studies provide evidence that BHT has a tumor-promoting effect,
especially for urethan and 2-AAF. On the other hand, as discussed in
Chapter 15, large amounts of BHT can inhibit neoplasia induced by a
number of chemicals*
There is no indication that BHA has any carcinogenic or tumor-
promoting activity. Its ability to inhibit neoplasia is discussed
in Chapter 15.
Vinyl Chloride
Containers made of polyvinyl chloride (PVC) are widely used for
packaging and storing foods. Since the appearance of reports linking
several fatal cases of a rare form of liver tumor with prolonged
industrial exposure to vinyl chloride, considerable attention has been
paid to the possible carcinogenicity and other toxic effects of the
monomer vinyl chloride, of which PVC is composed (Creech and Johnson,
1974; Nicholson ejt al. , 1975).
PVC is classified as an indirect food additive by the FDA, whereas
the monomer, which may be present at low levels as a residue in PVC, is
regarded as a contaminant (U.S. Consumer Product Safety Commission,
1974).
Vinyl chloride has been detected in a variety of alcoholic drinks
at levels ranging from 0.2 to 1 mg/liter (Williams, 1976a,b) and in
vinegars at levels as high as 9.4 mg/liter (Williams and Miles, 1975).
It has also been found in products packaged and stored in polyvinyl
chloride containers. For example, concentrations ranging from 0.05 to
14.8 mg/kg have been detected in edible oils (Rb*sli et_ al_. , 1975),
0.05 mg/kg has been detected in margarine and butter (Fuchs et^ al.,
1975), and 10.0 yg/liter is the highest concentration found in finished
drinking water in the United States (U.S. Environmental Protection
Agency, 1975a).
Epidemiological Evidence. There have been no epidemiological
studies on exposure to vinyl chloride as a food contaminant; however f
14-11
several investigators have studied the effect of occupational exposure.
In the United States, Creech and Johnson (1974) were the first to re-
port an association between inhalation exposure to vinyl chloride and
hepatic angiosarcomas. In a cohort study of males who had been occupa-
tionally exposed to vinyl chloride for at least 1 year* Tabershaw and
Gaffey (1974) observed an excess of cancer of the digestive system,
liver (mainly angiosarcoma) , respiratory tract, and brain, as well as
lymphomaso Nicholson et._ aJU (1975) noted a 2.3-fold excess of cancer
mortality among workers exposed for at least 5 years. Monson et al.
(1974) reported a 50% excess of deaths due to all cancers in workers
producing and polymerizing vinyl chloride. Several other studies have
indicated an association between exposure to vinyl chloride and in-
creased mortality from cancer at various sites (Duck and Carter, 1976;
Fox and Collier, 1977; Waxweiler et_ al . , 1976).
Experimental Evidence; Carcinogenicity* Male and female Sprague-
Dawley rats receiving gastric intubations of vinyl chloride in doses up
to 50 mg/kg bw developed mainly angiosarcomas and cancers of Zymbal's
gland (Maltoni, 1977; Maltoni et_ al . , 1975).
In lifetime feeding studies with Wistar rats, Feron et_ al. (1975,
1981) observed that vinyl chloride monomer in doses ranging from 1.7
to 14.1 mg/kg bw induced hepatocellular carcinomas, hepatic angiosar-
comas, pulmonary angiosarcomas, extrahepatic abdominal angiosarcomas,
tumors of Zymbal's gland, abdominal mesotheliomas, and adenocarcinomas
of mammary glands.
Inhalation exposures to vinyl chloride produced cancers of the lung,
mammary gland, and liver in mice (Maltoni, 1977); cancers of Zymbal's
gland, the liver, kidney, and brain in Spr ague-Da wley rats (Maltoni et
al* , 1974); and cancers of the liver, skin, and stomach in hamsters
TMaltoni, 1977; Maltoni t al. , 1974).
Experimental Evidence; Mutagenicity Tests and Other Short-Term
Tests'^ Vinyl chloride vapors induced mutations in Ames Salmonella
strains (Andrews e al . , 1976; Bartsch e al. , 1979), Escherichia
coli (Greim et_ ad. , 1975), Schizosaccharomyces pombe (Loprieno et
al. , 1976), Drosophila melanogaster (Verburgt and Vogel, 1977), and
mammalian cells (Huberman <et al. , 1975). They also induced gene
conversions in yeast (Eckardt et_ al^. , 1981).
Male workers occupationally exposed to vinyl chloride were reported
to have more chromosome aberrations than were observed in unexposed
cohorts (Funes-Cravloto et^ al. , 1975; Heath et^al., 1977; Purchase et
a^., 1975).
Summary and Conclusions. Occupational exposure to vinyl chloride
is associated with increased incidence of cancer of the liver, brain,
respiratory tract, and lymphatic system, but this evidence has been
derived from studies of groups occupationally exposed to high doses
of vinyl chloride. Similar carcinogenic effects were demonstrated in
rats that ingested or inhaled large amounts of vinyl chloride. These
results were later confirmed in mice and hamsters.
14-12
Vinyl chloride is mutagenic in bacteria, yeast, Drosophila, and
mammalian cells. It also has clastogenic effects on humans.
Acrylonitrile
Acrylonitrile is produced on a large scale in industry. Its
occurrence in foods as an "indirect" additive or contaminant may be
attributed to its use in food packaging and the migratory quality of
the monomer, which is present in small amounts in the polymer. For
example, in a preliminary analysis of three foods wrapped in acrylo-
nitrile-based packaging materials (margarine, olive oil, and bologna),
C. V. Breder (U.S. Food and Drug Administration, personal communica-
tion, 1980) detected acrylonitrile in concentrations ranging from 13 to
49 ng/kg.
Epidemiological Evidence* Exposure of the general public to
acrylonitrile could occur through migration of the residual monomer
In polymeric products in contact with food or potable water. The
significance of such exposure has not yet been evaluated. However,
a retrospective cohort study of 1,345 male employees possibly exposed
to acrylonitrile at a DuPont textile plant indicated that there was a
trend toward increased risk of cancer at all sites, especially the
lung. The risk was greater as the duration and amount of exposure
increased (O'Berg, 1980).
Experimental Evidence; Carcinogenicity. Rats receiving acrylo-
nitrile in drinking water In doses of 100 or 300 mg/liter for 12 months
developed stomach papillomas, tumors of the central nervous system, and
carcinomas of Zymbal's gland (Norris, 1977). In an inhalation study
with acrylonitrile, rats developed tumors of the central nervous system
and ear duct, as well as masses in the mammary region (Norris, 1977).
Experimental Evidence: Mutagenicity. Acrylonitrile induced
mutations in the Ames test in Salmonella strains TA1535, TA1538, and
TA78 (Milvy, 1978; Milvy and Wolff, 1977) and in E. coli (Venitt et
a 1 , 1977). But chromosome aberrations in workers exposed to acrylo-
nitrile for an average of 15.3 years did not exceed those in unexposed
controls (Thiess and Fleig, 1978).
Summary and Conclusions. There is no information on the health
effects resulting from the Ingestion of small amounts of acrylonitrile
monomer in the diet. Humans potentially exposed to acrylonitrile in a
synthetic fiber plant were found to be at an increased risk of cancer,
particularly of the lung, but there Is no further Information on this
subject. In experiments in rats, ingestion or inhalation of large
amounts of acrylonitrile enhanced tumors at several sites. This
limited evidence, combined with the finding that acrylonitrile is
mutagenic, suggests that acrylonitrile may be carcinogenic in humans.
14-13
Diethylstilbestrol (DBS)
Considerable attention has centered on the public health
consequences of drug residues in animal tissues consumed by humans.
Among the approximately 20 growth hormones commonly used in animal
feed, attention has mainly focused on diethylstilbestrol (DES), whose
residues have been monitored for many years following reports that
DES was carcinogenic in animals (Fitzhugh, 1964; Jukes, 1974). Until
June 1978, DES was permitted for use by humans as a control for func-
tional menstrual disorders; for prevention of postpartum breast en-
gorgement; as therapy for estrogen deficiencies associated with the
climacteric and other hormone-related conditions; as a "morning-after
pill"; and as chemotherapy for prostate cancer and for breast cancer
in postmenopausal women.
Until 1979, when the use of DES was terminated, it was also
permitted as a growth promoter for cattle and sheep under certain
conditions delineated by the FDA (Code of Federal Regulations, 1978;
U.S. Food and Drug Administration, 1979).
In 1972 and 1973, the U.S. Department of Agriculture detected DES
residues in beef liver at levels of 2 and 0.5 yg/kg, respectively
(Jukes, 1976; Mussman, 1975). Since 1973 no residues of DES have been
detected in 99.4% of a small number of beef livers sampled by methods
that have a detection limit of 0.5 yg/liter (Rurainski e al. , 1977).
Epidemiological Evidence. There are no reports of epidemiological
studies concerning the health effects of DES residues in food. Thera-
peutic doses of DES during pregnancy have been associated with an in-
crease in vaginal and cervical adenocarcinoma among the daughters of
DES users, primarily in those between the ages of 10 and 30 years
(Greenwald t al. , 1973; Herbst and Cole, 1978; Herbst e al . , 1972;
Hill, 1973).
Cases of breast cancer in men treated with DES for prostate cancer
have been observed after the start of the treatment (Billow et al* ,
1973). Of 24 female patients treated with DES for 5 years or more for
gonadal dysgenesis (Turner's syndrome), two developed endometrial car-
cinoma (Cutler ej^ l/> 1972), but the risk of endometrial carcinoma in
untreated patients is not known.
Experimental Evidence; Carcinogenicity. DES fed to C3H female
mice in concentrations ranging from 6.26 to 1,000 yg/kg diet produced
mammary carcinomas in increasing incidence with increased doses (Gass
et <a., 1964). At the highest doses (500 and 1,000 yg/kg diet), the
latent period was reduced from 49 weeks to 31 weeks. Male C3H mice
developed mammary carcinomas when fed DES at doses of 500 ]jg/kg diet
or more (Gass et al. , 1964) .
In C3H/An mice fed DES at and 250 yg/kg diet for 18 months, the
incidence of mammary cancers was significantly higher than in the
controls (Gass et_ al. , 1974) .
14-14
Sprague-Dawley rats fed DBS at 0.02 or 02 mg/kg bw In the diet
daily for 2 years developed pituitary tumors (males only), some
bepatomas (females only) 9 and mammary tumors (males and females)
(Gibson jet a!L. , 1967). In the progeny of pregnant Syrian golden
hamsters administered DBS by intragastric tube* there was a high
incidence of metaplastic, dysplastic, and neoplastic lesions in the
genital tract (Rustia, 1979; Rustia and Shubik, 1976) .
Experimental Evidences Mutagenicity and Other Short-Term Tests*
DES was not mutagenic in the Ames test with and without metabolic
activation (Glatt jet al . , 1979; McCann and Ames, 1976) and in . coll
(Fluck et al., 1976). It induced chromosome aberrations in Chinese
hamster~iroblasts (Ishidate and Odashima, 1977) and in murine bone
marrow cells in vivo (Ivett and Tice, 1981). In other studies, DES
induced mutations in mouse lymphoma cells (Clive, 1977), unscheduled
DNA synthesis in HeLa cells (Martin et_ al^. , 1978), and aneuploidy in
vivo in several strains of mice (Chrisman, 1974).
Summary and Conclusions. There is sufficient evidence that DES
used in therapeutic doses produces vaginal and cervical cancer in the
female offspring of treated women. In animals, it produces mainly
mammary tumors in various species.
ENVIRONMENTAL CONTAMINANTS
Environmental contaminants in food can be loosely divided into
three categories: some trace metals and organometalllc compounds,
some natural and synthetic radioactive substances, and some natural
and synthetic organic compounds. Only a few pesticides, two industrial
chemicals, and some contaminants falling into the third category are
discussed in this section.
Pesticides
Residues of pesticides often remain on agricultural commodities
after they have been harvested and prepared for consumer purchase.
They are also found in processed foods derived from these commodities.
Despite extensive exposure of the general population to low levels
of pesticides from numerous sources, especially foods and drinking
water, very little reliable information is available about their
effects on human health. Nevertheless, since many pesticides whose
residues are present in food are known or suspected of being carcino-
genic in some animal species, there is a basis for concern about their
potential effects on human health. Although the use of several organo-
chlorine compounds has been gradually suspended by the Environmental
Protection Agency, some concern is still warranted because they have
a propensity to persist In the environment, to accumulate in foods
14-15
commonly consumed by humans (U.S. Department of Health, Education, and
Welfare, 1969; U.S. Food and Drug Administration, 1980b) , and to con-
centrate in body tissues (International Agency for Research on Cancer,
1979).
The general population Is exposed to these compounds principally
through food and drinking water (International Agency for Research on
Cancer, 1979). As demonstrated by the Market Basket Surveys conducted
since the early 1960s by the FDA, the levels of pesticides In food are
very low and they vary only slightly from region to region. The organo-
chlorine compounds tend to accumulate in fat-containing foods such as
meat, fish, poultry, and dairy products, whereas the organophosphates
are generally more common In cereal products (U.S. Food and Drug Admin-
istration, 1980b).
This section focuses on only a few pesticides primarily, the
organochlorine insecticides and miticides, some organophosphates, and
two carbamate Insecticides. These compounds have been selected because
most of them are monitored regularly through the Market Basket Surveys
(U.S. Food and Drug Administration, 1980b), because they were or are
used widely and, therefore, present a greater probability for human
exposure, and because many of them, especially the cyclodienes and
their epoxides, are believed to be potentially hazardous to human
health (International Agency for Research on Cancer, 1974, 1979;
National Academy of Sciences, 1977).
Epidemiologlcal Evidence. Two cross-sectional studies were con-
ducted on workers engaged in the manufacture of dichlorodiphenyltrl-
chloroethane (DDT). In one, 40 men exposed to an estimated 10 to 40
mg DDT daily, mainly through inhalation or dermal contact over 1 to 8
years, showed no evidence of neoplasia (Ortelee, 1958). In the second,
no cases of cancer or blood dyscrasia were reported among 35 workers
exposed to 3 to 18 mg DDT daily for 11 to 19 years (Laws t al . , 1967).
More than 30 cases of aplastic anemia associated with exposure to
toxaphene, lindane, or benzene hexachloride have been reported (Inter-
national Agency for Research on Cancer, 1974; West, 1967; U.S. Environ-
mental Protection Agency, 1980). Jedli&ta ejt al. (1958) described a
family with two boys who developed leukemia 8 months after exposure to
lindane in an agricultural distribution center. Infante et. al. (1978)
reported 14 cases of neuroblastoma over a 16-month period. Of these,
five were in children who were unintentionally exposed pre- and
postnatally to chlordane formulations.
Wang and MacMahon (1979) reported that there was no overall excess
in mortality from cancer and no significant excess in deaths due to
lung cancer among 7,403 workers employed for 3 or more months in plants
manufacturing chlordane and heptachlor. However, no definitive conclu-
sions can be drawn because the population was small, and the period of
follow-up was short.
14-16
In a case-control study of 60 subjects and 120 controls, Wang and
Gruff erman (1981) found no correlation between the disappearance data for
various chlorinated hydrocarbons and mortality (during 1950-1975) from
aplastic anemia among workers engaged in occupations associated with such
exposure .
Jager (1970) and Versteeg and Jager (1973) reported a follow-up study
of 233 workers who were exposed to aldrin and dieldrin for as long as 17.!
years (average, 7.6 years). One death due to stomach cancer was reported
among the 181 workers still employed by the firm at the time of the study
in 1968.
The EPA conducted a survey of 199 workers exposed to toxaphene for an
average of 5.23 years between 1949 and 1977 (U.S. Department of Agricul-
ture, 1977). Among the 20 deaths that occurred, one was due to stomach
cancer.
Barthel (1976) reported a high incidence of lung cancer (11 cases
versus 0.54 expected) among 316 farm workers exposed to various pesticidei
including DDT, toxaphene, lindane (y-benzene hexachloride) , hexachloroben-
zene (HCB), and parathion for 6 to 23 years. Whether cancer was asso-
ciated with exposure to individual pesticides is difficult to determine
because the investigator did not control for smoking, and the workers wen
exposed to various chemicals simultaneously or alternately.
Experimental Evidence. Tables 14-1, 14-2, and 14-3 present the re-
sults of carcinogenicity and mutagenicity tests for some organochlorine
compounds, some organophosphates, and two carbamates. Only studies in
which the chemical was administered orally have been included in the
evaluation for carcinogenicity.
For most organochlorine pesticides, the evidence for carcinogenic-
ity is based on the production of parenchymal liver-cell tumors in
mice. With the exception of methoxychlor, which has not been found to
be mutagenic or carcinogenic, all other organochlorine compounds listed
in Table 14-1 appear to be weakly carcinogenic in mice. Results from
tests in rats indicate that toxaphene and Kepone (chlordecone) are
carcinogenic and that heptachlor (with chlordane) , hexachlorobenzene,
and lindane may be carcinogenic. Hexachlorobenzene also causes cancer in
hamsters.
In bioassays conducted by the National Cancer Institute (1978a,
1979b,c,d,e), the organophosphates malathion, methyl parathion, and
diazinon did not lead to an increase in tumor incidence in rats or mice
(Table 14-2). However, parathion resulted in an increased incidence of
cortical tumors of the adrenal gland in Osborne Mendel rats (National
Cancer Institute, 1979f). Parathion and diazinon were not mutagenic in
bacterial tests, but studies have indicated that parathion induces
chromosome abnormalities in guinea pigs (Dikshith, 1973) and that diazino
induces them in the lymphocytes of humans (Huang, 1973). Aldicarb is a
highly toxic compound, as indicated in Table 14-3, but it does not appear
14-17
to be carcinogenic in rats and mice. The data for carbaryl are inconclu-
sive and do not permit an assessment of carcinogenicity. However, carbaryl
is capable of reacting with nitrite under mildly acidic conditions (similar
to those present in the human stomach) to produce N-nitrosocarbaryl, which
is known to Induce cancer In rats (Eisenbrand !/> 1976; Lijlnsky and
Taylor, 1976). Although Ohshima and Bartsch (1981) have provided direct
evidence that nitrosamines can be formed In the human stomach, such infor-
mation should be interpreted with caution because the extent to which this
reaction could occur endogenously would depend on a number of factors,
including the differences In the concentration of the reactants, pH, and
the presence of catalysts and blocking agents.
The results of mutagenicity and related short-term tests for some
organochlorine pesticides did not coincide with data from experiments to
study carcinogenicity in animals. This disparity may Indicate the limited
value of mutagenicity tests for screening organochlorine compounds for
potential adverse effects.
Summary and Conclusions. Residues of a few organochlorine, organo-
phosphate, and carbamate pesticides are commonly detected in the diet,
generally at levels that are one to two orders of magnitude below their
Acceptable Daily Intake (ADI). Unlike the organophosphates and carba-
mates, most of the organochlorine compounds are metabolized slowly and
tend to accumulate in body tissues. The organochlorine compounds and the
organophosphates have the potential to modify the activity of microsomal
enzymes and to engage in synergistic interactions.
Data from the few epidemlological studies that have been conducted
permit no conclusion to be drawn about the carcinogenic risk to humans
exposed to pesticides.
The experimental data reviewed in this section Indicate the following:
A number of the common organochlorine pesticides to which the
general population is exposed cause cancer in mice and some In other
animal species.
With the exception of parathion, the organophosphate pesticides
discussed herein have not been found to be carcinogenic in laboratory
animals .
Of the two carbamates, aldicarb does not appear to be carcingenic
in rats or mice, and the data on the carcinogenicity of carbaryl are
Inconclusive. Carbaryl is capable of reacting with nitrite under mildly
acidic conditions to produce carcinogenic N-nitroso compounds. Such
nitrosation reactions have been shown to occur in the human stomach, but
the degree of risk they pose to human health is not known.
On the basis of studies in animals, and in the absence of adequate
data from epidemiological studies, it appears that Kepone (chlordecone) ,
14-18
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14-22
toxaphene, hexachlorobenzene, and, perhaps , heptachlor (with chlordane)
and lindane present a carcinogenic risk to humans. However, it is rea-
sonable to assume that the amounts present in the average U.S. diet do
not make a major contribution to the overall risk of cancer for humans.
Polychlorinated Biphenyls (PCB's)
Polychlorinated biphenyls (PCB's), which are complex mixtures of
chlorinated hydrocarbons, have been used for industrial purposes for the
past half century. With rare exceptions, commercial PCB f s are contami-
nated with low levels of toxic impurities such as polychlorinated di-
benzofurans and chlorinated naphthalenes.
The effects of PCB's on health have been reviewed recently by the
International Agency for Research on Cancer (1978) and the Subcommittee
on the Health Effects of Polychlorinated Biphenyls and Polybrominated
Biphenyls (1978). Initial concern about the adverse health effects of
various commercial PCB mixtures originated when chloracne and hepatic
changes were observed among workers engaged in the production of these
compounds (Schwartz, 1943). The gradual realization that PCB's are
highly toxic and exceedingly persistent in the environment led the U.S.
Environmental Protection Agency (1979) to suspend their manufacture and
use in commerce. Because of the extreme stability and high potential of
PCB's for assimilation in the food chain, the FDA has established limits
for their levels in different foods (U.S. Food and Drug Administration,
1977b).
For humans, the major source of exposure to low levels of PCB's
is diet. Generally, PCB's have been found only in the flesh or prod-
ucts of animals (e.g., fish, milk, eggs, and cheese) and in animal feed
derived from animal products (e.g., fish meal) (Jelinek, 1981; Jelinek
and Corneliussen, 1976). Between 1969 and 1975 the levels of PCB's de-
clined in all foods examined, except fish. Daily dietary intakes mea-
sured between 1974 and 1977 indicated that PCB's had dropped to levels
well below the tolerance levels in individual foods (U.S. Food and Drug
Administration, 1980b). PCB's also tend to accumulate In the adipose
tissue of humans, in milk, and In blood (Kutz and Strassman, 1976).
Epidemlologlcal Evidence. During a 9-year period in Japan (1968-
1975), there were reports of more than 1,200 cases of Yusho disease (a
disorder involving ocular, dermatological, and nervous symptoms) in humans
who had consumed rice oil accidentally contaminated with Kanechlor 400 (a
PCB) (Higuchi, 1976; Kuratsune elt al. , 1976). Nine out of 22 (41%) of the
deaths, which were reported as long as 5.5 years after the Initial
exposure, were due to malignant neoplasms (Kuratsune, 1976; Urabe, 1974).
However, the investigators did not compare this incidence with the rate
of expected deaths from various neoplasms in the population.
Bahn et al. (1976, 1977) reported two malignant melanomas among 31
workers C2U times the expected incidence) who had been heavily exposed to
14-23
Aroclor 1254 (a PCB) and possibly other chemicals, and one melanoma among
41 others who had been less heavily exposed. Three other workers in the
heavily exposed group were diagnosed as having four cancers at other
sites, including two in the pancreas.
Brown and Jones (1981) reported a retrospective study of 2,567 workers
employed for at least 3 months in plants using PCB's* The total mortality
from all causes and mortality from cancers were lower than expected, but
were slightly, although not significantly, excessive (3 vs. 1.07 expected)
for liver cancer.
Experimental Evidence A number of experiments have been conducted in
laboratory animals to test the carcinogenicity of various PCB's. Table
14-4 summarizes the results of some experiments in which various compounds
were administered orally to study their carcinogenicity, mutagenicity, or
their ability to act as tumor-promoting agents.
On the basis of data from the five experiments examined, it appears
that Kanechlor 500 and Aroclor 1254 induce cancer in mice and that Aroclor
1260 is carcinogenic in rats. All three compounds have induced benign and
malignant liver cell tumors in laboratory animals. From experiments in
which PCB's were tested as promoting agents, it appears that Kanechlor 400
and 500 enhance hepatocarcinogenicity of 3-methyl-4-aminoazobenzene (3 f -
DMAB) and N^-nitrosodiethylamine (NDEA) in rats and of lindane in mice,
whereas Kanechlor 500 when administered to rats simultaneously with the
carcinogen inhibited the hepatocarcinogenicity of 3'-DMAB, 2-AAF, and NDEA
(Makiura et al . , 1974) .
Aroclor 1221 and 1268 are mutagenic, and have been shown to induce
microsomal activation in the Ames test (Wyndham et^ al. , 1976). A number
of other PCB's, e.g., Aroclor 1254 (see Table 14-4), are negative in the
dominant lethal assay in rats and do not induce chromosome aberrations in
cultures of lymphocytes from humans. These findings are difficult to
interpret for Aroclor 1254, which induces dose-related hepatocellular
carcinoma in female rats and enhances NDEA-induced hepatocellular
carcinoma in rats (Preston et_ aJU , 1981).
Summary and Conclusions. PCB's are highly persistent in the environ-
ment and have been detected in human tissues. They occur in fish, meat,
and dairy foods in amounts that are well below the tolerance levels estab-
lished by the FDA.
Limited data from epidemiological studies suggest that exposure to
high levels of PCB's may be associated with the development of malignant
melanomas, but no conclusion can be drawn about the risk to humans from
exposure to PCB-contaminated foods. Results of laboratory experiments
indicate that some PCB f s are carcinogenic in rodents, producing mostly
tumors of the liver at doses much higher than those generally present in
the average U.S. diet. Recent evidence indicates that some PCB's may act
primarily as tumor-promoting agents.
14-24
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14-25
Polybrominated Biphenyls (PBB's)
Polybrominated biphenyls (PBB's), which are chemically related to the
PCB's, have been used as flame retardants in industrial processes. Like
PCB's, PBB's persist In the environment and can accumulate in body fat.
/ Epidemiological Evidence* Studies of a population accidentally
exposed to PBB's in Michigan in 1973 indicated that the exposure was
associated with a number of adverse effects on health (Kay, 1977; Office
of Technology Assessment, 1979); however, because of the short Interval
between the time of exposure and the measurement of effects, these
studies could provide no definitive information about the relationship
between PBB's and cancer.
Experimental Evidence. Sherman rats given a single oral dose of
PBB's by gavage developed neoplastic liver nodules after 6 months
(Kimbrough t_ al . , 1978). In a follow-up study, Sherman rats were
given a single large dose of PBB's or 12 divided doses by gavage. Both
treatments resulted in a high Incidence of hepatocellular carcinomas.
In the rats given multiple high doses, the incidence of tumors was higher
and some of the liver carcinomas were less differentiated than in rats
given the single dose (Kimbrough et_ auL. , 1981).
Recently, Aust has shown that PBB's are tumor promoters In rats
(S. D. Aust, Michigan State University, personal communication, 1981).
The doses given in this iri vivo assay ranged from 1 to 100 mg/kg diet.
PBB's did not induce mutations in the Ames test and in Chinese
hamster uterine cells (Aust, personal communication, 1981). When
administered orally to mice at doses ranging from 50 to 500 mg/kg bw,
they did not induce chromosome aberrations In bone marrow cells (Wertz
and Flcsor, 1978).
Summary and Conclusions. These studies indicate that single doses or
short-term treatment with PBB's can induce liver tumors In rats. There
is some Indication that the effect is dose-dependent, but the number of
rats given the lower doses was small. Because of the lack of data from
epidemiological studies, it is difficult to determine the significance of
these findings for human health.
Polycyclic Aromatic Hydrocarbons (PAH's)
Polycyclic aromatic hydrocarbons (PAH's) are organic compounds
containing two or more benzene rings. To date, more than 100 of these
compounds have been identified in the environment and In foods (Lo and
Sandi, 1978; U.S. Environmental Protection Agency, 1975c). Of these,
less than 20 have been shown to cause cancer in laboratory animals, and
only five of these have induced cancer following oral administration:
benzo[a]pyrene (BaP), dibenz[a,h]anthracene (DBA), benz [aj anthracene
14-26
3-methylcholanthrene (3-MCA), and 7 ,12-dimethylbenzIaJ anthracene
(7,12-DMBA). Of these, 3-MCA and 7,12-DMBA are synthetic chemicals
that do not occur normally In the diet*
The major sources of the PAH contamination of food are curing smokes,
contaminated soils, polluted air and water, and endogenous biosynthesis
by plants and microorganisms* The methods with which foods are cooked or
processed also affect the PAH content of the foods (Howard and Fazio,
1980; Lo and Sandi, 1978).
The contamination of foods by PAH's is widespread* These compounds
have been detected in fresh meats, smoked fish and meats, grilled and
roasted foods, leafy and root vegetables, vegetable oils, grains, plants,
fruits, seafoods, whiskies, etc* Smoking of meat increases the total PAH
burden (Howard and Fazio, 1980). Similarly, hot air drying and roasting
are potential sources of contamination of grain and coffee (Fritz, 1969).
Most foods contain very low levels of PAH's, but shellfish seem to concen-
trate these compounds and are unable to metabolize them* Various PAH's,
including BaP, benzanthracene, and chrysene, have been detected in Scotch,
bourbon, and Japanese whiskies at extremely low levels, ranging from 0.03
to 0.08 yg/liter (Masuda ^ al. , 1966). Leafy plants such as spinach,
kale, and tobacco contain higher levels of BaP (Grimmer, 1968), and only
a small fraction (^10%) appears to be removed by washing (Grimmer, 1968).
Although BaP constitutes only between 1% and 20% of the total amount
of carcinogenic PAH f s in the environment, there is a great deal of Infor-
mation on the levels of that compound in various foods (Suess, 1976). In
contrast, the information on the levels of other .carcinogenic PAH's is
still fragmentary. Fritz (1971) estimated that the average annual Intake
of BaP in the German Democratic Republic ranged from 340 to 1,200 yg per
person annually. In Hungary, it was calculated to be 290 to 612 yg/ per-
son annually (Soos, 1980). The main sources of ingested BaP were vege-
tables and fruits, whereas the smoked foods contributed only a minor
fraction of the total BaP Intake. Although there is information concern-
ing the levels of BaP In specific foods, such as oils and smoked meats,
the total Intake of BaP from all sources In the United States has not
been reported.
Epidemiological Evidence* Evidence concerning the association
between cancer in humans (mainly cancer of the skin and lung) and
exposure to PAH's derives from studies of humans exposed occupa-
tionally to PAH's in soot from chimneys, coal tar, creasote oil, and
other petroleum products (Butlin, 1892; Doll et al*, 1972; Heller,
1930; Kennaway and Kennaway, 1947; Pott, 177577
There is little Information concerning the relationship between
ingestion of PAH-contaminated food and cancer in humans. In one study,
Hajdu (1974) observed that the incidence of stomach cancer among the
Vend population living in West Hungary is significantly higher than the
incidence for the general Hungarian population* The Vend population
14-27
routinely consumes home-smoked meat products that contain substantially
higher BaP levels than found in samples of smoked food consumed in other
parts of Hungary (Soos, 1980). In another report, Dungal (1961) specu-
lated that the high incidence of gastric cancer in the northwestern part
of Iceland may be associated with the frequent consumption of smoked
trout and smoked mutton, which were found to contain relatively high
concentrations of PAH's. In Latvia, Voitalovich jet al. (1957) reported
that the Incidence of gastrointestinal cancer over a 5-year period was
significantly higher in a coastal region than in a nearby inland region*
They attributed this difference to occupational exposures in the fishing
industry (e.g., during the smoking of fish), frequent consumption of
smoked fish, and poorly balanced diet. However, these Investigators
(Dungal, 1961; Soos, 1980; Voitalovich e_t al. , 1957) did not take into
consideration the potential effect of nitrite or KHnitroso compounds,
which may also be present In such foods and which are also believed to
be associated with gastric cancer.
Experimental Evidence; Carcinogenicity and Mutagenicity. The PAH's
exert their toxic, carcinogenic, and mutagenic effects only after being
metabolized by the mixed-function oxidases of various tissues (Freudenthal
and Jones, 1976). Their carcinogenic activity varies from very weak to
potent. Some of the PAH's have been shown to be carcinogenic to mice,
rats, hamsters, rabbits, and monkeys when administered topically, orally,
or parenterally (Freudenthal and Jones, 1976). Many PAH's have also been
.found to be mutagenic. The discussion below is limited to those PAH's
generally detected in foods and found to be carcinogenic when administered
orally.
Benzo[J pyrene
The carcinogenicity of BaP in various animal species has been well
established. A single 0.2 mg dose of BaP administered intragastrically
produced forestomach tumors in mice (Peirce, 1961). In other studies,
mice fed a diet containing BaP at 250 mg/kg developed an increasing
number of forestomach tumors as the duration of the experiment was ex-
tended (Neal and Rigdon, 1967), and mice exposed for 140 days developed
lung tumors and leukemia in addition to forestomach tumors (Rigdon and
Neal, 1969).
In Spr ague-Da wley rats, a single dose of 100 mg BaP resulted In the
induction of mammary tumors (Huggins and Yang, 1962). Hamsters fed BaP
at 500 mg/kg diet 4 days/week for up to 14 months developed esophageal,
intestinal, and stomach tumors (Chu and Malmgren, 1965).
BaP has been also shown to be mutagenic to Ames Salmonella strains
(Hollstein et_ aJU , 1979; Nagao and Suglmura, 1978), to be genotoxic In
the hepatocyte primary culture-DNA repair test (Tong je al . , 1981), to
induce mutations In the epithelial cells of the liver of rats (Tong et,
al. , 1981), and to Induce transformations in Syrian golden hamster embryo
cells (Casto, 1979).
14-28
Dibenz [,h janthracene
Dietary administration of DBA for 5 to 7 months (total dose,
9-19 mg/animal) resulted in the appearance' of forestomach tumors in
mice after 1 year (Larionov and Soboleva, 1938). Mice receiving the
compound at 0.2 mg/ml in an olive oil emulsion, which was substituted
for their drinking water, received an average dose of 0.76 to 0.85
mg/day. Pulmonary adenomatosis developed in these animals after 200
days. In addition, females in this group developed mammary carcinomas
(Snell and Stewart, 1962). Administration of DBA by stomach tube to
several strains of mice (total dose, 15 mg/mouse administered over 15
weeks) resulted in a significant increase in mammary carcinomas
(Biancifiori and Caschera, 1962).
DBA was positive in the Ames test (McCann et a_l. , 1975). Treatment
of hamster embryo cells with DBA increased the frequency of transforma-
tions induced by the simian adenovirus SA7 (Casto, 1979).
Benz [ a ] anthracene
Administration of 0.5 mg BA in mineral oil by stomach tube at
intervals of 3 to 7 days induced papillomas of the forestomach in mice
(Bock and King, 1959). Mice receiving 15 doses of 1.5 mg BA each for 15
weeks by stomach tube developed lung adenomas, hepatomas, and forestomach
papillomas (Klein, 1963).
BA has been shown to be mutagenic in the Ames test (Hollstein e al. ,
1979; McCann et_ al. , 1975). It was also positive in the prophage induc-
tion test (Morreau t_ al. , 1976) and genotoxic in the hepatocyte primary
culture-DNA repair test (Tong e al . , 1981).
Summary and Conclusions. Low levels of many PAH's are present as
contaminants in a variety of foods. Smoking and broiling of foods and
the use of curing smokes contributes to the PAH content of foods. Of
the more than 100 PAH's found in the environment, approximately 20 are
carcinogenic in laboratory animals. Of the five PAH's found to be
carcinogenic when administered orally, three (BaP, DBA, and BA) occur
in the average U.S. diet.
Occupational exposure of humans to PAH f s is associated with an
increased incidence of skin and lung cancer. There is no reliable
information about the consumption of foods contaminated with low levels
of PAH's and the development of human cancer. Some investigators have
speculated that a high incidence of stomach cancer in Hungary and Iceland
could be associated with consumption of smoked meat and fish, which are
potential sources of PAH's and/or nitrosamines and their precursors, but
this has not been conclusively demonstrated. However, since studies in
animals have shown that PAH's are carcinogenic when administered orally,
and occupational exposure to substances containing PAH's has been asso-
ciated with skin and lung cancer, it would be prudent to minimize the
dietary exposure to PAH's.
14-29
OVERALL SUMMARY AND CONCLUSIONS
Food Additives
Nearly 3,000 substances are intentionally added to process foods
in the United States. Another estimated 12,000 chemicals, such as
vinyl chloride and acrylonitrlle, which are used in food-packaging,
are classified as indirect additives. Some additives, such as sugar,
are consumed in large amounts by the general population. However, the
annual per capita exposure to most of these substances constitutes a
minute portion of the diet. Although the Food Safety Provisions and,
In many cases, the Delaney Clause of the Federal Food, Drug, and Cos-
metic Act prohibit the addition of known carcinogens to foods, only a
small proportion of substances added to foods have been tested for
carcinogenicity according to protocols that are considered acceptable
by current standards. Moreover, except for the studies on nonnutritive
sweeteners, very few epidemiologlcal studies have been conducted to
examine the effect of food additives on cancer Incidence.
Of the few direct food additives that have been tested and found to
be carcinogenic in animals, all except saccharin have been banned from
use in the food supply. Minute residues of a few indirect additives that
are known either to produce cancer in animals, e.g., vinyl chloride and
acrylonitrile, or to be carcinogenic in humans, e.g., vinyl chloride, are
occasionally detected in foods. There is no evidence suggesting that the
increasing use of food additives has contributed significantly to the
overall risk of cancer for humans. However, the lack of detectable
effect may be due to the relatively recent use of these substances, to
their lack of carcinogenicity, or to the inability of epidemiologlcal
techniques to detect the effects of additives against the background of
common cancers from other causes. Therefore, no definitive conclusion
can be reached until more data become available.
Environmental Contaminants
Very low levels of a large and chemically diverse group of sub-
stances environmental contaminants may be present in a variety of
foods. The dietary levels of some of these substances are monitored by
the FDA Market Basket Surveys. Many of these contaminants have been
extensively tested for carcinogenicity.
The results of standard chronic toxicity tests indicate that a
number of environmental contaminants (e.g., some organochlorine pesti-
cides, poly chlorinated biphenyls, and polycyclic aromatic hydrocarbons)
cause cancer in laboratory animals. There is no epidemiological evidence
to suggest that these compounds individually make a major contribution to
the risk of human cancer. However, the possibility that they may act
synergistically and may thereby create a greater carcinogenic risk cannot
be excluded.
14-30
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CHAPTER 15
INHIBITORS OF CARCINOGENS SIS
In recent years, a number of foods and constituents of foods have
been studied for their inhibitory effects on carcinogenesis. Results
from both epidemiological and experimental studies have indicated that
some of the substances studied do have inhibitory effects, but the
mechanisms are not yet clear.
This chapter contains a review of the most conclusive data pertain-
ing to the inhibitory effects of nonnutritive constituents of the diet.
EPIDEMIOLOGICAL STUDIES
Epidemiological studies have produced data suggesting that certain
substances in foods may protect against the development of cancer. A
substantial number of these studies have demonstrated an inverse re-
lationship between consumption of vegetables and risk of cancer, es-
pecially cancer of the gastrointestinal tract. Vegetables contain
nutritive constituents with inhibitory capacities (as discussed in
Section A and Chapter 9) as well as nonnutritive inhibitors, which are
described in this chapter. The epidemiological data are not sufficient
to permit a definition of the individual roles played by each of the
several putative inhibitors that may be present in the same food. Never-
theless, the data are of considerable interest even though the mechanism
of inhibition is unclear.
In one study of stomach cancer, Graham et al. (1972) found that con-
sumption of raw vegetables, including cole slaw and red cabbage, was
higher among controls than among cases. In a study of Hawaiian Japanese,
Haenszel et al. (1972) reported lower risk of stomach cancer for con-
sumers of~everal Western vegetables, many of which are eaten raw. In a
corresponding study in Japan, the same investigators reported a lower
risk of stomach cancer for consumers of lettuce and celery (Haenszel t
al. , 1976). In case-control studies conducted in Norway and in the
United States (Minnesota), Bjelke (1978) also demonstrated an inverse
relationship between incidence of stomach cancer and the indices for
consumption of vegetables, especially among younger patients and women.
He also reported preliminary findings from a prospective cohort study,
showing a reduced risk of stomach cancer for consumers of large amounts
of vegetables in Norway, but not in the United States. In Japan,
Hirayama (1977) found that the risk for stomach cancer was lower for
nonsmokers who ate green and yellow vegetables than for nonsmokers who
did not eat these vegetables.
15-2
Much of the epidemiological evidence pertains to cancer of the large
bowel. Modan t_ al. (1975) compared cases of colon and rectal cancer
with both hospital and neighborhood controls and found an inverse associ-
ation between colon cancer (but not for rectal cancer) and the frequent
consumption of fiber-containing foods, including cabbage* Other inverse
associations between consumption of fiber-containing foods and colon
cancer (see Chapter 8) could also reflect different intakes of crucif-
erous vegetables. Graham e l. (1978) reported that a decreased risk
for colon cancer was associated with frequent ingestion of raw vegeta-
bles, especially cabbage, brussels sprouts, and broccoli, in a case-
control study conducted in New York State. Similar but less impressive
findings were obtained for rectal cancer.
Haenszel et al. (1980) found an inverse association for cabbage con-
sumption in a~ase^control study of colorectal cancer in Japan, but not
in Hawaii (Haenszel et al. , 1973). In the previously cited, ongoing
cohort study in Minnesota and Norway, Bjelke (1978) noted that the risk
for colorectal cancer is associated inversely with an index of vegetable
consumption in Minnesota, but not in Norway. This result paralleled his
earlier finding that the intake of vegetables, particularly cabbage, by
colorectal cancer cases was less than for controls in Minnesota.
EXPERIMENTAL STUDIES
As discussed in Chapters 8, 9, and 10, certain vitamins, minerals,
and fiber have been found to inhibit some forms of carcinogenesis. Dur-
ing the past decade, studies have shown that foods also contain nonnutri-
tive organic compounds that are also inhibitors of carcinogenesis. These
compounds fall into a category frequently referred to as "secondary plant
constituents." Among these constituents are phenols, indoles, aromatic
isothiocyanates, flavones, protease inhibitors, and the plant sterol
g-sitosterol, which are discussed below along with related studies of the
effects of individual foods.
Effects of Selected Chemicals
The administration of selected chemicals in this category has been
shown to inhibit both initiation and promotion of chemically induced
neoplasia in virtually all organs of laboratory animals. As will become
apparent in subsequent discussions, much remains to be learned about
these numerous and virtually omnipresent dietary constituents, including
their possible adverse as well as beneficial effects.
The mechanisms by which these compounds prevent neoplasia is incom-
pletely understood. Some inhibitors, so-called "blocking agents," exert
their effects when administered before and during exposure to carcinogens-
Others act during the promotion phase of carcinogenesis, and still others
15-3
inhibit only when given following exposures to inhibitors and promoters
from other external sources. Finally, some inhibitors are effective at
more than one point during the process of carcinogenesis. Of the In-
hibitors Identified thus far, the largest number falls into the category
of blocking agents, appearing to act by preventing carcinogens or their
metabolites from reaching or reacting with critical target sites. In
many instances, they alter the activity of enzyme systems that metabolize
carcinogenic agents (Wattenberg, 1980).
A second general form of Inhibition is particularly relevant to pro-
motion. The inhibitor is assumed either to suppress free radical forma-
tion resulting from exposure to tumor promoters or to trap these radi-
cals. Protease inhibitors and phenolic antioxidants have been postulated
to inhibit neoplasia in this manner.
The fact that a compound inhibits chemically induced carcinogenesis
in laboratory animals should not be interpreted as indicating that an
increased intake of the substance is desirable for humans. Knowledge of
possible adverse effects of these compounds is Incomplete (see discussion
at the end of this chapter) .
Phenols. Two categories of phenolic Inhibitors of carcinogenesis
are found in food. One is synthetic and the other occurs naturally. The
synthetic antloxidant, butylated hydroxyani sole (BHA) is a widely used
food additive and has been extensively studied for its capacity to in-
hibit carcinogenrinduced neoplasia (Wattenberg, 1978). Table 15-1 lists
experiments in which BHA has been shown to have inhibitory effects. In
these studies, BHA was administered before and/or during exposure to the
carcinogen. BHA has also been shown to Inhibit host-mediated mutagenesis
resulting from exposure to hycanthone, metrifonate, praziquantel, and
metronidazole (Batzinger e al. , 1978). Slaga (1981) reported that BHA
Inhibited tumor promotion in the mouse skin when administered after the
carcinogen.
Studies of the mechanism by which BHA inhibits chemically induced
carcinogenesis have shown that this phenolic compound produces a co-
ordinated enzyme response that may be interpreted as causing a greater
rate of detoxification (Wattenberg, 1980). Mice that have been fed BHA
for 1 to 2 weeks in carcinogen inhibition experiments show marked in-
creases in both glutathione S-transf erase activity and tissue glutathione
levels (Benson jet jd. , 1978, 1979). Glutathione S-transf erase is an
important enzyme for detoxifying chemical carcinogens (Benson et al. ,
1978; Jakoby, 1978; Wattenberg, 1980). The activity of uridine diphos-
phate (UDP)-glucuronyl transf erase, which Is another Important conjugat-
ing enzyme In the detoxification systems, is also increased (Cha and
Bueding, 1979). The feeding of BHA has also been reported to increase
epoxide hydrolase activity (Cha ej^ al. , 1978) and to alter the microsomal
monooxygenase system (Lam et_ ali , 1980; Speier e_t_ al.. , 1978).
15-4
TABLE 15-1
Inhibition of Carcinogen-Induced Neoplasia by BHA a
Carcinogen Inhibited
Species
Mouse
Site of Neoplasm
Benzo[a]pyrene
Lung
Benzofa]pyrene
Mouse
Forestomach
Benzo [a]pyrene-7-8-dihydrodiol
Mouse
Forestomach, lung, and
lymphoid tissue
7, 12-Dimethylbenz [a]anthracene
Mouse
Lung
7 , 12-Dimethylbenz [a] anthracene
Mouse
Forestomach
7,12-Dimethylbenz [a] anthracene
Mouse
Skin
7 , 12-Dimethylbenz [a] anthracene
Rat
Breast
7-Hydroxymethyl-12-methyl-
benz [a] anthracene
Mouse
Lung
Di benz [a. , h. ] anthracene
Mouse
Lung
Nitrosodiethylamine
Mouse
Lung
4-Nitroquinoline-N-oxide
Mouse
Lung
Uracil mustard
Mouse
Lung
Urethan
Mouse
Lung
Methylazoxymethanol acetate
Mouse
Large intestine
tans-5-Amino-3-[2-(5-nitro~2-
f ury l)viny 1 ] -1 , 2 , 4-oxadiazole
Mouse
Forestomach, lung,
and lymphoid tissue
a From Wattenberg, 1979a.
15-5
The amount of BHA consumed in the average U.S. diet Is estimated
to be several milligrams per day at most. This level, when corrected
for body weight , is far less than that given to laboratory animals in
experimental studies. However* exposure to carcinogens is almost cer-
tainly orders of magnitude lower in the human population than in ex-
perimental studies in animals. No conclusion can be drawn at this
time as to whether inhibitory effects of BHA occur at the low concen-
trations of carcinogens to which humans are generally exposed.
Recent studies have shown that several naturally occurring phe-
nolic compounds inhibit carcinogenesis In mice (Wattenberg e t a 1 . ,
1980) . The phenols studied thus far are cinnamic acid derivatives
that are common constituents of plants. They include o-hydroxy cinna-
mic acid, -hydroxycinnamic acid, 3,4-dihydroxycinnamic acid (caffeic
acid), and~4-hydroxy-3~methoxycinnamic acid (ferulic acid). Limited
data on these derivatives indicate that their inhibition of benzo[a.]~
pyrene-induced neoplasia in the mouse is considerably weaker than that
of BHA (Wattenberg auU , 1980). There are many other phenols in
plants, including plants consumed by humans, but their inhibitory
activity is unknown.
Indoles. Indole-3-acetonitrile, 3, 3 f -diindolylmethane, and
indole-3-carbinol are found in edible cruciferous vegetables such
as brussels sprouts, cabbage, cauliflower, and broccoli. Indole-3-
acetonitrile is the most abundant of the three. These indoles have
been studied for their effects on neoplasia induced by benzo[ajpyrene
(BaP) and 7,12-dimethylbenz [a.] anthracene (DMBA) In rodents (Wattenberg
and Loub, 1978). When added to the diet of mice before and during ad-
ministration of BaP, all three Indoles inhibited BaP-induced neoplasia
of the f orestomach and pulmonary adenoma formation. In other experi-
ments, indole-3-carbinol and 3,3 f -diindolylmethane inhibited DMBA-
induced mammary tumor formation in female Sprague-Dawley rats. Indole-
3-acetonitrile was Inactive In the rat (Wattenberg and Loub, 1978).
The original rationale for testing the three Indoles stemmed from
their ability to alter microsomal monooxygenase oxidase activity. All
three compounds increased the activity of this enzyme system (Loub et.
al. , 1975; Pantuck e al. , 1976) indole-3-carbinol and 3,3'-di-
indolylme thane more strongly than indole-3-acetonltrile. The three of
them also increased glutathione S-transf erase activity. There have
been no studies in which these compounds were administered after the
carcinogen.
Aromatic Isothiocyanates. Benzyl isothiocyanates and phenethyl
isothiocyanate are also constituents of cruciferous plants. These
aromatic isothiocyanates have been shown to inhibit neoplasia induced
by polycyclic aromatic hydrocarbons (PAH's) when they were adminis-
tered during the initiation phase under several different experimental
conditions. These results were obtained when the aromatic isothio-
cyanate was fed both before and during administration of the PAH 1 s
15-6
(Wattenberg, 1977, 1979b). Little is known about their mechanism of
inhibition other than the fact that benzyl isothiocyanate is a potent
inducer of glutathione S-transf erase activity. In further studies,
mammary tumor formation resulting from exposure to DMBA was inhibited
by the administration of benzyl isothiocyanate subsequent to the car-
cinogen. It has also been demonstrated that this compound inhibited
1,2-dimethylhydrazine-induced neoplasia of the large intestine when
the exposures were begun 1 week after administration of the carcinogen
(Wattenberg, 1981). The mechanism of these inhibitory effects is not
known.
Flavones. The study of flavones (found in fruits and vegetables)
as possible inhibitors was undertaken as a result of data showing that
several inducers of increased microsomal mixed function oxidase acti-
vity inhibit chemically induced carcinogenesis.
Inhibition of BaP-induced carcinogenesis has been studied with
three flavones: two synthetic compounds B-naphthof lavone (5,6-
benzoflavone) and quercetin pentamethyl ether and one naturally
occurring compound rutin (3,3 T ,4' ,5,7-pentahydroxyflavone-~3-
rutinoside). Quercetin pentamethyl ether is sometimes substituted
for tangeretin, a naturally occurring pentamethoxy f lavone found in
citrus fruits. All three flavones induce aryl hydrocarbon hydroxylase
(AHH) activity: g -naphthof lavone is the most potent inducer, quercetin
pentamethyl ether is a moderate inducer, and rutin has the weakest
inducing capacity. When added to the diet of A/HeJ mice subsequently
challenged with orally administered BaP, 8-naphthof lavone caused
almost total inhibition of pulmonary adenoma formation, and quercetin
pentamethyl ether reduced the number of these neoplasms by one-half.
The number of adenomas was the same in animals fed rutin and the con-
trol diet. Thus, the inhibitory effects of BaP-induced neoplasia
paralleled the potency of the three flavones in Inducing increased AHH
activity (Wattenberg and Leong, 1968, 1970). Recently, 6-naphthof la-
vone has been shown to induce activity of conjugating enzymes, includ-
ing glutathione Stransf erase.
The mutagenic flavones have multiple hydroxyl groups. Flavones
exerting protective effects do not have free polar groups; they either
contain methoxy substituents or are unsubstituted (MacGregor and Jurd,
1978). The mutagenic and carcinogenic effects of flavones are dis-
cussed in Chapter 13.
Protease Inhibitors. Protease inhibitors are widely distributed
in plants, and are particularly abundant in seeds. Soybeans, a major
source of protein in many vegetarian diets, and lima beans contain a
variety of these compounds.
Protease inhibitors have in common the ability to inhibit pro-
tease enzymes as well as tumor promotion (Troll, 1980). Inhibition of
this type has been demonstrated using the two-stage model to study
15-7
skin carclnogenesis in the mouse. In addition, a reduced incidence
of breast cancer has been observed in irradiated rats fed a diet rich
in protease inhibitors after exposure to the radiation (Troll, 1980).
Protease inhibitors have also been shown to block promotion in in
vitro systems. The transformation of C3H10T1/2 cells by x-rays~Tol~
lowed by incubation with 12-oj"tetradecanoylphorbol-13-acetate (TPA) is
blocked if protease inhibitors are present after exposure to the radi-
ation (Kennedy and Little, 1981). Troll (1980) suggested that pro-
tease inhibitors prevent formation of free radicals by tumor promoters.
Since BHA and some related antioxidants inhibit promotion, there may
be common mechanisms -among inhibitors that would lead to synergistic
effects.
g-Sitosterol. 3-Sitosterol is a common plant sterol that is pres-
ent in many different vegetables and vegetable oils. Its protective
effects have been studied in an experimental system with N-nitroso-
methylurea a direct-acting carcinogen. 3-Sitosterol reduced the in-
cidence of large bowel cancer from 54% to 33% when fed in the diet
through the entire course of the experiment or only during the promo-
tion phase of carcinogenesis (Cohen and Raicht, 1981; Raicht _e t al . ,
1980). Other plant sterols of similar structure have not been studied
for potential inhibitory effects.
Effects of Individual Foods on Carcinogen-Metabolizing Enzyme Systems
Studies in Animals. Several enzyme systems involved in metaboliz-
ing carcinogens are highly responsive to compounds entering the body
from the environment. For example, animals fed purified diets and
kept in filtered air show almost no monooxygenase oxidase activity for
PAH f s and azo dyes in the small bowel and lungs (Wattenberg, 1970,
1972).
One source of naturally occurring inducers of increased microsomal
monooxygenase activity is vegetables. In laboratory animals, crucif-
erous vegetables such as brussels sprouts, cabbage, cauliflower, and
broccoli have a moderately potent inducing effect on monooxygenase
oxidase activity. Other vegetables such as alfalfa, spinach, and
celery have some inducing activity, but it is weak (Wattenberg, 1972).
More recently, studies have been conducted to examine the effects
of individual foods on glutathione S-transf erase, which is a major
detoxification system that catalyzes the binding of a vast variety of
electrophiles to the sulfhydryl group of glutathione (Chasseaud, 1979;
Jakoby, 1978). Since the reactive ultimate carcinogenic forms of chem-
icals are electrophiles, the glutathione S-transf erase system takes on
considerable importance as a mechanism for carcinogen detoxification.
Enhancement of the activity of this system, as measured in vitro, has
been shown to be associated with decreased response of tissues to
chemical carcinogens (Sparnins and Wattenberg, 1981).
15-8
The activity of glutathione S-transferase is much greater In tis-
sues of animals fed normal rather than purified diets* Diets contain-
ing large quantities of cruciferous vegetables induce increased gluta-
thione S-transferase activity (Sparnins, 1980)* The extent to which
green coffee beans induce such activity Is quite remarkable. In mice
fed a diet containing green coffee beans, glutathione S-transferase
activity was enhanced sixfold in the liver and sevenfold in the small
bowel (Sparnins et^ aJU , 1981). Considerably less inducing activity
has been found in roasted coffee beans, commercial Instant coffee, and
instant decaffeinated coffee, Indicating that some destruction of the
inducing compounds has occurred during processing. Two potent inducers
of glutathione S-transferase activity have been isolated from green
coffee beans. These compounds are kahweol palmitate and cafestol
palmltate (Lam et al , 1982)
Studies In Humans. Diets containing large amounts of cabbage and
brussels sprouts were fed to healthy volunteers between 21 and 32 years
of age* The effects of this diet on the metabolism of antipyrine and
phenacetin were studied. These compounds, like many carcinogens, are
initially metabolized by the microsomal monooxygenase system and their
oxidative metabolites subsequently conjugated. The results indicated
that subjects eating diets rich in vegetables metabolized both drugs
more rapidly than did subjects on a control diet (Pantuck et al.,
1979).
Possible Adverse Effects of Inhibitors
Several of the inhibitors discussed above, e.g., Indole-3-carbinol
and 3,3 f -diindolylmethane, are moderate or strong inducers of micro-
somal monooxygenase activity. Compounds with this characteristic are
potentially hazardous (Wattenberg, 1979a). For example, the micro-
somal monooxygenase enzyme system produces two different categories of
carcinogen metabolites: detoxification products and activated species.
In the metabolism of aromatic amines, ring hydroxylation results In de-
toxification, whereas hydroxylation of the nitrogen leads to the forma-
tion of a proximate carcinogen. Thus, administration of compounds that
Increase monooxygenase activity can result in competing reactions, and
the net effect Is uncertain.
A second possible adverse effect of compounds that induce micro-
somal monooxygenase activity is that they may act as tumor promoters.
An additional consideration is that the microsomal monooxygenase sys-
tem metabolizes some physiological compounds such as steroid hormones.
This alteration of activity might cause adverse effects by changing
the levels of these compounds or their metabolites.
Two compounds have been shown experimentally to have dual effects,
i.e., they can inhibit carcinogenesis and they also can cause or en-
hance neoplasia. One such compound is butylated hydroxy toluene (BHT).
This compound can inhibit carcinogenesis under certain conditions. It
is also a tumor promoter, as discussed in Chapter 14. The second com-
pound is coumarin, which can inhibit carcinogenesis, but when fed to
15-9
rats for 18 months, it produces bile duct carcinomas. Thus, a particu-
lar compound may have diverse effects. When this occurs, its overall
impact is difficult to predict.
SUMMARY
Epidemiological Studies
Epidemiological evidence from several case-control studies
suggests that certain vegetables, especially cruciferous vegetables,
have a possible protective effect against cancer at several sites.
The responsible constituent or constituents cannot be identified on
the basis of present information.
Experimental Studies
Food contains many compounds that have been shown to inhibit
carcinogenesis in laboratory animals. Because there are so many of
these compounds and because their nature is so diverse, they are
likely to be present in the diet of most humans.
The mechanisms of inhibition are incompletely understood. Some
inhibitors modify the activity of enzyme systems that have the capa-
city to detoxify carcinogenic agents. Others may act by suppressing
formation of free radicals or by trapping free radicals arising during
the process of carcinogenesis.
A number of compounds inhibiting chemically induced carcinogenesis
in laboratory animals are present in cruciferous vegetables. These
compounds include aromatic isothiocyanates, indoles, and phenols.
CONCLUSION
The committee concluded that there is sufficient epidemiological
evidence to suggest that consumption of certain vegetables, especially
carotene-rich (i.e., dark green and deep yellow) vegetables and cru-
ciferous vegetables (e.g., cabbage, broccoli, cauliflower, and brussels
sprouts), is associated with a reduction in the incidence of cancer at
several sites in humans. A number of nonnutritive and nutritive com-
pounds that are present in these vegetables also inhibit carcinogenesis
in laboratory animals. Investigators have not yet established which,
if any, of these compounds may be responsible for the protective effect
observed in epidemiological studies.
The fact that a compound has been shown to inhibit carcinogen-
induced neoplasia in laboratory animals should not be interpreted as
indicating that it is desirable for humans. These compounds may have
adverse effects. Information on this subject is incomplete.
15-10
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SECTION C
PATTERNS OF DIET AND CANCER
In Sections A and B the committee reviewed the evidence concerning
the role of specific nutrients and nonnutritive dietary components.
This section provides a more comprehensive assessment of the overall
contribution of diet to cancer.
Chapter 16 contains an overview of the evidence relating diet to
cancer in light of the trends in cancer incidence and mortality and the
influence of other environmental factors on these trends. In Chapter
17, the epidemiological evidence is reassembled by each cancer site to
provide a perspective on the contribution of all dietary factors to the
occurrence of cancer at specific sites.
The committee recognized at the start that the current state of
knowledge is insufficient to permit a precise quantification of the
effect of the diet on the incidence of cancer. Therefore, in Chapter
18, the committee has presented merely a framework for assessing risk,
with particular emphasis on the different elements that need to be con-
sidered when assessing the risks posed by initiators and modifiers that
may be present in the diet. Attempts made by other investigators to
determine the quantitative contribution of diet to the overall risk of
cancer are also discussed.
CHAPTER 16
CANCER INCIDENCE AND MORTALITY
A number of authors (e.g., Doll, 1967, 1977; Higginson, 1969;
HIgginson and Muir, 1979; Wynder and Gori, 1977) have pointed to the
large differences in cancer incidence and mortality that exist between
countries and the likelihood that these differences are largely due to
environmental factors. Here the term environment is used in its widest
sense, encompassing all factors external to humans, as distinct from
differences that are attributable to man's genetic makeup* Higginson
(1969) calculated the proportion of cancers that were theoretically pre-
ventable and suggested that approximately 90% of all cancers in humans
are influenced by exogenous factors. This observation has stimulated
attempts to distinguish between occupation and way of life (Fox and
Adelstein, 1978) and to identify those components linked to lifestyle
(Higginson and Muir, 1979; Miller, 1981) specifically, to examine diet
as a component of lifestyle (Miller e al . , 1980; Wynder and Gori, 1977).
This chapter reviews those aspects of descriptive epidemiology that
indicate the importance of dietary factors in explaining differences in
cancer Incidence and mortality among various population groups. In gen-
eral, Incidence data are used when available, since they more directly
relate to etiology* being uninfluenced by changes in survival due to
advances In the management and treatment of cancer. In the absence of
incidence data, mortality data have been used. As pointed out by Doll
and Peto (1981), mortality data have certain advantages as well. Their
Interpretation is less often complicated by changes in diagnostic prac-
tices or cancer registration.
The diet is generally associated with cancers of the gastrointestinal
tract (I.e., esophagus, stomach, colon, rectum, pancreas, and liver) and
cancers of some sex-hormone-responsive sites (I.e., breast, prostate,
endometrlum, and ovary). There is also evidence that diet Is associated
to some degree with cancers of the respiratory system and bladder. Inci-
dence data for 1973-1977, as compiled by the National Cancer Institute
Surveillance, Epidemiology, and End Results (NCI-SEER) Program (Young et
al., 1981), indicate that cancer of the stomach, colon, breast, bladder,
and prostate comprise ^ 39% of the cancers in males and ^43% of cancers
In females. Thus, these presumably diet-sensitive sites account for
approximately 40% of the cancers in both sexes (Young e al , 1981). If
we add the incidence of lung cancer In males, which may be influenced by
diet as well as by smoking, the total for cancer in males reaches 60%.
GEOGRAPHICAL DIFFERENCES RELATED TO ETHNICITY
In the United States, incidence data for whites and blacks have been
compared. Table 16-1 provides such comparisons for gastrointestinal
16-2
TABLE 16-1
Cumulative Incidence Rate (Age 0-74) per 100 Persons for
Malignant Neoplasms in All Areas of the United States
(Excluding Puerto Rico), 1973-1977*
Site
Whites
Blacks
Males
Females
Males
Females
Esophagus
0.5
0.2
1.7
0.4
Stomach
1.1
0.4
2.1
0.9
Colon
3.1
2.7
3.2
2.7
Rectum and rectosigmoid
1.8
1.0
1.4
1.0
Liver
0.2
0.1
0.5
0.2
Gallbladder
0.1
0.1
0.1
0.1
Pancreas
1.1
0.7
1.7
1.1
Lung
7.7
2.3
11.5
2.4
Breast
0.1
8.2
0.1
7.0
Corpus uteri
3.1
1.4
Ovary
1.4
0.9
Prostate
5.2
9.6
Bladder
2.4
0.6
1.2
0.5
Kidney
0.9
0.4
0.8
0.4
a Data from Young et al. , 1981.
16-3
cancers and for some other sites (Young et al., 1981). The measure used
(i.e., cumulative incidence to age 74) is an approximation of the life-
time risk of developing cancer of that site in the absence of death from
other causes (Day, 1976). Rates are higher for blacks of both sexes for
cancers of the esophagus, stomach, liver, and pancreas, and there is a
substantial excess of prostate cancer in black males. However, the inci-
dence of bladder cancer is lower in blacks.
A number of cancer registries provide incidence data for different
racial groups (Waterhouse et_ al. , 1976). For example, the age-adjusted
rates for stomach and large bowel cancer among Chinese living in the San
Francisco Bay area are similar to those for whites, whereas rates for
prostate and bladder cancer are lower. In Hawaii, the rates for stomach
cancer are higher for Hawaiians and Japanese of both sexes and for
Chinese and Filipino females than the corresponding rates for Caucasians
(Table 16-2) (Young e^ al. , 1981).
The differences in the rates of cancer among racial and ethnic
groups do not necessarily have a ready interpretation. Some, such as
the similarity of rates among the various ethnic groups (Henderson et
al. , in press) suggest the possibility of a genetic contribution to
cancer at some sites. However, other explanations should also be
considered. Most of the differences would indicate that cultural and,
thus, environmental factors are involved in the etiology of cancers at
the various sites. Among these, dietary factors are likely to be of
critical importance.
CHANGES SUBSEQUENT TO MIGRATION
The hypothesis that differences in cancer incidence and mortality
among racial or ethnic groups are due largely to cultural rather than
genetic factors receives considerable support from data on groups that
have migrated (Haenszel, 1961; Kmet, 1970). In general, the incidence of
cancer in migrant groups is similar to that of the country of origin or
is intermediate between that of the country of origin and the host coun-
try. After one or more generations, it becomes the same as that of the
host country. These trends have been well documented for gastric, colon,
and breast cancer in Japanese who migrated to Hawaii and to the western
continental United States and Canada (Buell, 1973; Kolonel et_ al. , 1980);
Eastern Europeans who migrated to the United States and Canada (Kmet,
1970); Icelanders who migrated to Manitoba, Canada (Choi et^ aJU , 1971);
and Southern Europeans who migrated to Australia (McMichael e al. , 1980),
The changes seem to be most rapid for colon cancer and somewhat less
rapid for stomach cancer. They are slowest for breast cancer, requiring
more than one, or possibly two, generations for a full effect to be mani-
fested. These different rates of change may reflect differences in the
stage of life during which factors exert an effect, or they may reflect
the differences in the action of carcinogenic initiators or promoting
agents.
16-4
TABLE 16-2
Average Annual Age-Adjusted Incidence (per 100,000) in
Different Ethnic Groups in Hawaii, 1973-1977 a
Race
Site
Sex
Hawaiian
Caucasian
Chinese
Filipino
13.3
7.3
Japanei
47.3
19.9
Stomach
M
F
51.4
23.9
15.6
7.0
14.6
9.4
Colon
M
F
20.2
17.5
33.8
24.4
39.3
28.2
24.3
13.2
36.5
24.4
Rectum and
rectosigmoid
M
F
15.9
10.9
17.6
10.2
20.6
11.0
16.5
10.0
28.2
11.0
Liver
M
F
12.6
9.7
2.9
1.9
10.3
3.6
13.3
2.1
7.5
2.8
Gallbladder
M
F
2.3
1.5
0.9
3.3
2.2
2.4
1.0
1.4
2.2
Pancreas
M
F
12.9
9.2
11.4
8.7
11.5
7.6
8.6
1.8
11.7
6.1
Breast
F
104.3
99.9
64.1
29.2
51.3
Corpus uteri
F
40.4
41.5
33.4
17.3
22.4
Ovary
F
11.8
10.7
8.1
5.4
8.0
Prostate
M
66.3
86.7
40.0
46.9
54.1
Kidney and
pelvis
M
F
5.8
5.5
13.5
3.0
2.9
4.6
4.7
3.8
6.1
2.5
Bladder
M
F
6.8
8.3
31.3
5.2
9.9
1.5
10.8
5.6
13.7
4.8
a Data from Young et al. , 1981.
16-5
When interpreting the effects of migration, it is important to recog-
nize that migrants are not necessarily representative of the population
from which they were derived. They may have led more active lives or have
a socioeconomic background that is not typical for the general population
in their country of origin, or they may have come from a specific region
with atypical characteristics. Furthermore, migrant groups may retain
some cultural habits, possibly Including different dietary practices,
while in their host country, even after several generations. MacDonald
(1966) compared the diet of 65 Japanese men, age 50 or more who had
migrated to Canada 35 to 55 years before, with 65 non- Japanese control
subjects. The Japanese ate more fish and rice than did the control group
and ingested less beef, potatoes, bread, milk, and cereals other than
rice. Fruit and vegetable consumption was similar In the two groups.
Hence, there may be differences in cancer incidence among groups from
different countries for some time after they migrated. In the United
States, breast cancer in postmenopausal women has been linked to German
ethnicity (Blot et_ al. , 1977b) . Mortality from colon and rectal cancer
is elevated in counties in the United States where there are large popu-
lations with Irish, German, or Czechoslovakian descent (Blot et al. ,
1976). Mortality from renal cancer is also elevated In counties where
a large percentage of the population is of German, Scandinavian, or,
especially, Russian descent (Blot and Fraumeni, 1979).
Where differences have been explored In detail, the findings support
the operation of environmental factors, as distinct from those of genetic
origin, even when "genetic isolates" are considered (Gaudette et al. ,
1978; Martin et al. , 1980).
CHANGING TIME TRENDS IN INCIDENCE AND MORTALITY
For various reasons, cancer Incidence and mortality In the United
States are reported neither completely nor accurately. Generally speak-
ing, although reporting of incidence has improved during the past 25
years, reporting is probably more accurate and complete for mortality.
There have also been recent improvements in the reporting of categories
of cancer. Therefore, long-term trends must be Interpreted cautiously,
and even recent trends are the subject of controversy.
Because of population growth and changes in its age distribution,
the annual number of cancer cases Is steadily Increasing in the United
States. For 1981, approximately 400,000 cancer deaths are projected,
and about 800,000 new cases expected to occur. Cancer is the second
most frequent cause of death (about 20% of total deaths). Against a
background of drastic environmental modification and rapid technologi-
cal change, some have suggested that a vast cancer "epidemic" may have
begun. However, since more people are living longer and cancer rates
16-6
are higher among older people, adjustment for age corrects the Impres-
sion that cancer rates are being driven upward dramatically by an in-
creasing environmental threat. In fact, examination of recent age-
adjusted rates indicates that there has been little change overall,
although there are some Increases and decreases in cancer incidence at
certain sites.
Apart from the smoklng-associated cancers, stomach cancer, and cer-
vical cancer, the incidence of and mortality from cancer at nearly all
sites have remained remarkably stable for the last 30 to 40 years (Devesa
and Silverman, 1978; Miller, 1980). There has been a slight increase in
the rates of nonrespiratory cancers for white males age 75 or more (but,
if anything, a decrease at ages 55-59 and 40-44). For other age groups,
the rates have been stable In females, there has been an increase in
the 74-84 age group, but decreases in the age groups 85 or more, 70-74,
and 40-54, and a relative stability for other age groups. The data
Indicate that rates for the youngest age groups (especially for women)
appear to be falling. This is a critical observation because the
youngest age groups would have been expected to show the effect first if
the environment were becoming increasingly carcinogenic.
There has been an increased incidence of breast cancer, especially in
postmenopausal women, but there has been little or no change in mortality
from cancer at this site (Barclay et_ al_. , 1975; Cutler t_ al_. , 1971; Fabia
^_t aJ. , 1977; Grace ejt al. , 1977). This finding Is probably due to a com-
bination of factors. For example, improved cancer registration has pro-
vided a more accurate reflection of cancer incidence. Furthermore, in-
creased awareness by the general population and physicians and Intensi-
fied pathological examination of resected tissue have led to early detec-
tion and, thus, slightly more successful treatment.
In Iceland, the age-specific curves for breast cancer have shifted
from higher rates for premenopausal women (similar to the pattern in
Japan in this century) to higher rates for postmenopausal women (similar
to the pattern in North American women) (Bjarnason et^ juU , 1974). How-
ever, an analysis of the data by birth cohort demonstrated that the shapes
of the age-specific curves were the same and that the incidence at each
age increased in successive birth cohorts. This suggests that the inci-
dence of breast cancer may have increased because more recent birth co-
horts were exposed to environmental factors that Increase the risk of
breast cancer.
The incidence of endometrial cancer increased remarkably during the
1970 f s, then fell sharply beginning in 1976, especially on the west coast
of the United States. There now seems to be little doubt that these
changes are due to the excessive use and then partial withdrawal of con-
jugated estrogens at the time of menopause ( Jick eit a.1. , 1980). Despite
the dramatic changes in incidence, mortality has remained stable.
16-7
Both incidence of and mortality from stomach cancer have declined
steadily in Western countries during the past 30 to 40 years (Devesa and
Silverman, 1978; Miller, 1980)* More recently, they have started to
decline in Japan (Hirayama, 1977).
These trends and stabilities are reflected in international incidence
data, apart from minor fluctuations due to changing registration practices
(Stukonis, 1978).
Recently, controversy has arisen over whether the general incidence
of cancer has been increasing significantly over the past several dec-
ades, in particular during the past 5 years. Resolution of this contro-
versy is complicated by the inadequacies in the data and by the different
trends for specific cancer sites. If lung and skin cancer are excluded
(the former because most of it is attributed to cigarette smoking, the
latter because it is easily curable and poorly reported), the remaining
aggregated cancer incidence appears to be roughly stable up to 1971.
Differences of interpretation have arisen from the comparison of SEER
data (collected after 1973) with the earlier data because they represent
different population samples and different methods of data collection.
Thus, Pollack and Horm (1980) suggested that cancer incidence is
rising in the United States, even for cancers not associated with
smoking. Their report was based on data from the third National Cancer
Survey (1959-1971) and the SEER Program for 1973-1976. Although the
authors took pains to exclude methodological reasons for the increase
and to regard it as real, it still seems possible that most of the ob-
served increases are artifactual, caused by more efficient registration
following the change from the earlier methods of a one-time survey to
those of a permanent registration system. The matter should be resolved
In the next few years as SEER data continue to accumulate.
INTERS ITE CORRELATIONS OF INCIDENCE
Burkitt (1971) pointed out that similar frequencies for different
diseases might imply common etiological factors. Using data from the
third National Cancer Survey (Cutler and Young, 1975), Winkelstein et al.
(1977) studied the geographic variation in the occurrence of cancers at
sites common to both sexes and at five sex-specific sites. They found
strong correlations among the incidence rates for cancer at three gastro-
intestinal sites, i.e., cancers of the colon and rectum were directly cor-
related with each other, and inversely correlated with stomach cancer.
In addition, there was a strong direct correlation between colorectal
cancer and bladder cancer in both men and women. There was also a strong
direct correlation among cancer of the breast, corpus uteri, and ovary in
women. These two groups of interrelated sites were also correlated with
one another.
Berg (1975) pointed out that international incidence rates for the
hormone-dependent cancers (i.e., breast, corpus uteri, and ovarian can-
cers in females and testis and prostate cancers in males) were closely
16-8
correlated with the rates for large bowel cancer* Table 16-3 shows the
extent to which the the cancer incidence rates for certain sites are
intercorrelated. The lowest correlation between males and females was
found for esophageal cancer; the highest, for colon cancer* Significant
direct correlations within the same sex occur for colon and rectal cancer
and for both sites combined with pancreatic cancer- There are significant
inverse correlations for colon and stomach cancer. In men, esophageal
cancer is directly correlated with liver cancer; in women, liver cancer
is inversely correlated with colon and rectal cancer* Colon and, to a
lesser extent, rectal and pancreatic cancers are directly correlated with
breast, endometrial, and ovarian cancers in women.
ASSOCIATIONS WITH SOCIQECQNQM1C STATUS
Using data for 1950 to 1969, Blot _et^ a.1 . (1977a) analyzed mortality
in the United States by county. This study has provided a number of
opportunities to evaluate mortality rates by socioeconomic status, which
may reflect differences in diet. Thus, mortality from colon and rectal
cancer has been associated with higher income and education levels (Blot
et al , 1976); mortality from breast cancer in postmenopausal women has
een linked to higher socioeconomic status (Blot e juL. , 1977a); and
mortality from renal cancer has been directly correlated in both sexes
with higher socioeconomic status (Blot and Fraumeni, 1979).
In the United Kingdom, the Regis tar General's Decennial Supplement
for England and Wales (Registrar General 1 s Office for England and Wales,
1978) and a report by Fox and Adelstein (1978) have shed further light on
the relative importance of socioeconomic status and occupational factors.
Standardization for social class has shown that nearly all significantly
high standardized mortality ratios for occupational groups are reduced to
nonsignificance after social class is considered. Fox and Adelstein
(1978) have calculated that occupation accounts for approximately 12% of
the variation in cancer mortality between social class groups, and that
lifestyle accounts for 88%. The corresponding proportions for all causes
of death are 18% and 82%, respectively.
Teppo e ! (1980), using data from the Finnish Cancer Registry,
reported an association between social class and cancer at a number of
sites. They found inverse correlations between social class and cancer
of the lip and stomach in males and direct correlations between social
class and colon cancer in both sexes and breast and lung cancer in
females. After examining the incidence of breast cancer by province and
selected municipalities in Finland, Hakama &t^ auU (1979) reported an
association with taxable income. They conclude? that factors reflected
by the standard of living and fertility might act independently.
16-9
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16-10
Urban-rural differences in cancer incidence and mortality have long
been recognized as indicators of the effect of socioeconomic status and
lifestyle. However, only the Norwegian Cancer Registry routinely reports
its data in this form, since reports are grouped according to the offi-
cial administrative boundaries (Waterhouse e j^L. , 1976). In urban areas,
there is a marked excess of esophageal and liver cancer in males and of
lung cancer in both sexes and a moderate excess of colon and pancreatic
cancer in males, breast cancer in females, and bladder and other urinary
tract cancers in both sexes. In rural areas, there is a marked excess of
lip cancer in males.
RELIGIOUS PRACTICES AND CANCER INCIDENCE AND MORTALITY
Religious groups whose lifestyles and dietary habits differ from
those of the general population have been a fruitful source for assessing
the possible effect of dietary variables.
Phillips and colleagues have studied Seventh-Day Adventists (SDA's),
a religious group with approximately 600,000 members in North America
(Phillips, 1975; Phillips et^ al . , 1980b). SDA's abstain from smoking
and drinking, and approximately 50% of them follow a lacto-ovovegetarian
diet. In earlier studies, Phillips (1975) suggested that the lacto-
ovovegetarian diet may protect against colon cancer; the evidence for
breast cancer was less clear. These studies compared cancer mortality
among California SDA's with mortality data for the general California
population. In more recent analyses, Phillips et^ al^ (1980a,b) used as
a non-SDA control group Californians who enrolled in a concurrent pro-
spective study conducted among the general population by the American
Cancer Society. This study showed that the risk of dying from colorectal
cancer and cancers related to smoking is clearly lower among SDA's than
among non-SDA' s of comparable age, sex, and socioeconomic status. The
risk of dying from breast cancer was also reduced, but not significantly.
This may be clarified in further analyses that take into account im-
portant risk factors for breast cancer. But since a number of SDA's are
adult converts, their risk of breast cancer may have been at least par-
tially determined by exposures in early (adolescent or young adult) life,
before they adopted SDA practices. However, the SDA age-specific mor-
tality curve for breast cancer is consistent with those of other low
risk populations, in which postmenopausal women have been observed to
have a lower risk for cancer at this site (Phillips !/> 1980b).
The Mormons comprise another religious group whose lifestyle differs
markedly from that of the general U.S. population. For at least 80
years, these members of the Church of Jesus Christ of Latter-Day Saints
have proscribed the use of alcohol, tobacco, coffee, and tea in all forms
to help ensure good health (Lyon et al., 1980). In addition, they recom-
mend a well-balanced diet, especially the use of grains, fruits, and
vegetables, and moderate consumption of meat (Enstrom, 1980). In a study
16-11
based on data from the Utah Cancer Registry, Lyon t al . (1976) reported
that the incidence of cancers associated with cigarette smoking; breast,
uterine, cervical, and ovarian cancer in females; and stomach cancer in
males was much lower in Mormons than in non-Mormons* Colon cancer was
also significantly lower in females, but not in males. In an update of
these analyses (Lyon et_ al. , 1980), the same reductions were observed,
but for colon and rectal cancer they had become significant for both
sexes* In states adjacent to Utah (Idaho and Wyoming), mortality from
smoking-*associated cancers and from cancers of the rectum and breast is
almost identical to that of Utah (Rawson, 1980) . Thus, there may be some
general environmental variable peculiar to this entire area affecting
cancer incidence and mortality.
In India, cancer incidence differs among religious groups, especially
between the Parsi and Hindu communities of Bombay (Jussawalla, 1976). In
the Parsi community, the rates of colon, rectal, and breast cancer are
substantially greater than those in the Hindu population, although they
are not as high as those In Western countries.
There are many differences other than dietary factors between
religious groups and the general population. Although attempts have
been made to control for the nondletary differences (e.g., Phillips et^
al. , 1980b), studies of groups will probably never be as effective as
direct evaluations of the effect of dietary factors and other variables
in individuals. Nevertheless, these studies of subgroups of the popula-
tion have value because they Indicate which hypotheses should be evalu-
ated more directly by other means.
CORRELATIONS OF INCIDENCE AND MORTALITY WITH DIETARY AND OTHER VARIABLES
In several studies, dietary and other variables have been found to be
strongly correlated with geographical differences In the incidence of and
mortality from cancer at a number of sites (Armstrong and Doll, 1975;
Carroll, 1975; Knox, 1977). Armstrong and Doll (1975) correlated inci-
dence rates for cancer at 27 sites in 23 countries and mortality rates
for cancer at 14 sites in 32 countries with a wide range of dietary and
other variables. They reported strong correlations between dietary vari-
ables and cancer at several sites, especially meat and fat Intake with
cancers of the colorectum, breast, corpus uteri, and ovary. Direct cor-
relations with dietary variables were also found for cancer of the small
intestine (sugar), pancreas (eggs, animal protein, and fat), and ovary
and bladder (fats and oils); inverse associations were reported for gas-
tric cancer (meat, animal protein, and fat) and cervical cancer (total
protein and fruit). Many of the dietary variables were strongly inter-
correlated, especially fat and protein of animal origin, and were also
correlated with gross national product. Carroll (1975) observed a strong
correlation between per capita intake of dietary fat and age-adjusted
mortality from breast cancer. The correlation was strongest for total
16-12
fat, almost as strong for animal fat, but almost completely absent for
vegetable fat. Knox (1977) suggested that associations between alcohol
intake and cancer of the mouth and larynx, between total fat intake and
cancer of the large intestine and breast, and between beer intake and
cancer of the rectum were causal- In Japan, Hirayama (1977) found that
the intakes of fat and pork were associated with mortality from breast
cancer in 12 different prefectures* After having reviewed data for
cancer and fat intake, Enig et_ al (1979) retracted their original
suggestion that cancer was correlated with the intake of total fat and
vegetable fat, but not with animal fat.
One disadvantage of this type of study, especially in relation to
breast and gastric cancer, is that current dietary factors are usually
correlated with current information on incidence and mortality, whereas a
more appropriate time relationship might be established by taking dietary
information recorded some 20 or 30 years ago and correlating it with
current incidence or mortality rates (Miller et_ aJU , 1980)*
By conducting personal interviews with 4,137 subjects to determine
their usual weekly food consumption, Kolonel et al * (1981) determined
the average daily consumption of several components of fat in the diets
of the five main ethnic groups in Hawaii. The intake of total fat
correlated with the ethnic-specific incidence rates of breast cancer
in Hawaii, but not with colon or prostate cancer incidence* There was
no correlation between cholesterol consumption and incidence of colon
cancer. One possible difficulty with this study is that many of the
means of dietary intake for the different ethnic groups were rather
close. Furthermore, current diet as measured in this study may not be
relevant to current incidence, especially for sites where incidence is
changing.
Evidence associating fiber intake with certain cancer sites has also
been contradictory. Drasar and Irving (1973) were unable to find any
association of breast and colon cancer incidence with per capita fiber
intake using data from 37 countries, although they demonstrated a high
correlation with fat and animal protein intake. However, the Interna-
tional Agency for Research on Cancer Intestinal Microecology Group (1977)
found that differences in dietary fiber in Scandinavian populations
appeared to correlate well with incidence of and mortality from colon
cancer.
Dietary correlation studies have produced evidence for groups, rather
than for individuals. Although the variation in the intake of nutrients
is great internationally, it is not necessarily extensive for groups
within countries. The variation of incidence and mortality within coun-
tries may also be low. Furthermore, the dietary information is generally
derived from food disappearance data (i.e., per capita intake), and not
necessarily from individual food consumption data. Hence, lack of cor-
relation, either nationally or internationally, does not suffice to dis-
prove a hypothesis. Conversely, one should not rely too heavily on ob-
served correlations in case they are confounded by some factor that could
not be studied or has not yet been identified (St,avraky, 1976).
16-13
ASSOCIATIONS WITH OTHER DISEASES
Burkitt (1971) noted an association between a number of chronic dis-
eases and "affluence/' He suggested that such "diseases of affluence"
might have a common etiology and that dietary fiber may play a role in
protecting against such illnesses as cancer of the colon and other sites,
coronary heart disease, diverticulitis, etc. There has been a recent
decline in mortality from ischemic heart disease In the United States,
Australia, and Canada, but not in the United Kingdom (Dwyer and Hetzel,
1980)* This decline has been associated by some Investigators with in-
creased consumption of polyunsaturated fats and reduced cigarette smok-
ing* We may therefore question why there has not been any indication of
a reduction in cancers associated with dietary components, especially
fat- Since the amount of vegetable fat in the U.S. diet has been in-
creasing (Page and Friend, 1978), one possible explanation could be that
such fat has an adverse influence on colorectal and breast cancer inci-
dence (Enig et_ jal. , 1978). An alternative explanation might be that the
substitution of polyunsaturated fats for saturated fats may help to re-
duce cardiovascular diseases, but for this substitution to have an effect
on fat-associated cancers, a concurrent reduction in total fat consump-
tion may also be necessary (Miller et al* , 1980) . It Is also possible
that any effect of fat on cancer incidence would take longer to appear
than its effect on cardiovascular disease; however, in view of the rapid
changes in colorectal cancer rates after migration, this appears to be an
unlikely explanation for cancer at this site. Finally, dietary changes
may not have had any influence on changes in cardiovascular disease.
SUMMARY
The incidence of cancers differs greatly among countries and to a
limited extent within countries. Studies of migrants (e.g., Japanese who
migrated to the United States) suggest environmental causes for these
differences. In affluent countries, stomach cancer rates have fallen,
rates for intestinal and breast cancer are stable, and pancreatic cancer
rates, which have increased, are now descreasing for males. The Inci-
dence of cancer of the colon, rectum, breast, corpus uteri, ovary, and
prostate are directly correlated with each other, but cancer of the colon
or rectum is inversely correlated with stomach cancer. Mortality from
colorectal and breast cancer Is directly associated with socloeconomic
status, and stomach cancer is inversely associated. In males, incidence
of cancer of the esophagus, liver, colon, pancreas, and lung is higher in
urban areas. Seventh-Day Adventists and Mormons have a low risk for
colon and breast cancer. Internationally, the Intake of fat has been
directly correlated with cancer of the breast, colon, rectum, pancreas,
corpus uteri, and ovary.
16-14
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CHAPTER 17
THE RELATIONSHIP OF DIET TO CANCER AT SPECIFIC SITES
To present more clearly what is known about the relationship between
diet and cancer at specific sites, the committee has reassembled the
epidemiological literature and summarized it by site: esophagus, stomach,
colon and rectum* liver, pancreas, gallbladder, lung, urinary bladder,
kidneys, breast, endometrium, ovary, and prostate. Since most of these
data have already been discussed in earlier chapters on specific dietary
constituents, the information contained in the following pages has been
greatly condensed. The organization of this chapter reflects the design
of most epidemiological studies, which generally examine cancer at spe-
cific sites.
ESQPHAGEAL CANCER
The incidence of esophageal cancer varies widely among different
regions of the world. A belt of particularly high risk runs from the
Middle East (notably the Caspian littoral of Iran) through central Asia
to China. Other regions of high risk are the eastern and southern areas
of Africa, and France has unusually high rates, especially in Normandy
and Brittany.
Correlational analyses have shown direct associations of alcohol
drinking with incidence of and mortality from esophageal cancer in
some parts of the world. These studies were based on both estimated
per capita intakes and dietary interview data in special population
groups in Western countries (Breslow and Enstrom, 1974; Hinds et al. ,
1980; Kolonel e al. , 1980; Lyon e al. , 1980a,b; Schoenberg et al. ,
1971). Chilvers e al. (1979) found a consistent relationship between
mortality from esophageal cancer and total ethanol intake in England
and Wales. Other investigators reported high correlations of esopha-
geal cancer mortality with death rates from cirrhosis and alcoholism.
(Lipworth and Rice, 1979; Tuyns e al. , 1979).
The results from a number of case-control studies have confirmed
the association with alcohol. Various investigators have demonstrated
a dose-response relationship after controlling for cigarette smoking
(Keller, 1980; Martinez, 1969; Pottern t al. , 1981; Tuyns et al . ,
1979; Williams and Horm, 1977; Wynder and Bross, 1961; Wynder and
Stellman, 1977). Schmidt and Popham (1981) found a significantly in-
creased risk for esophageal cancer in a retrospective cohort study of
male alcoholics. Smoking and alcohol appear to act synergistically to
increase the risk for esophageal cancer as they do for cancers of the
oral cavity and larynx (Rothman and Keller, 1972; Tuyns et^ al . , 1977).
17-2
There has been no consistency in the type of alcoholic beverage most
strongly associated with the risk of esophageal cancer. Some investi-
gators found no specificity at all (Breslow and Enstrom, 1974; Williams
and Horm, 1977); some found a stronger association with hard liquor than
with beer or wine (Pottern et_ al^ , 1981; Wynder and Bross, 1961); and
some reported a stronger association with beer (Hinds et_ al_. , 1980;
Mettlin t al. , 1980).
Alcohol consumption cannot explain the pattern of esophageal cancer
in Africa and Asia (Bradshaw and Schonland, 1974; Burrell, 1962; Collis
t al.. , 1971; GateijrtaJL. , 1978; Higginson and Oettle, 1960; Joint
Iran- International Agency for Research on Cancer Study Group, 1977; Yang,
1980). Correlation studies have indicated that the intakes of pulses
(e.g., lentils), green vegetables, fresh fruit, animal and fish protein,
and the estimated intakes of vitamin A, vitamin C, and riboflavin, are
lower in high risk regions of the Caspian littoral in Iran (Hormozdiari
et al. , 1975; Joint Iran- International Agency for Research on Cancer
Study Group, 1977). Similar studies in China have implicated low intakes
of trace elements (particularly molybdenum), animal products, fat, fruits,
vegetables, calcium, and riboflavin; high intakes of pickles, pickled
vegetables, and moldy foods containing N-nitroso compounds (possibly
produced by the fungal contaminants); and consumption of foods at very
high temperatures (Coordinating Group for Research on Etiology of Esopha-
geal Cancer in North China, 1975; Yang, 1980). In Japan, Segi (1975)
found a direct association between mortality from esophageal cancer and
the intake of tea-cooked rice gruel. On the other hand, Stocks (1970)
and Howell (1974) found no associations between international per capita
food and beverage intakes and corresponding mortality rates for esophageal
cancer.
In view of the findings that nitrosamines and fungi contaminate some
foods in China, it is notable that Marasas e al^. (1979) found higher
contamination levels of Fusarium mycotoxins in samples of corn (a dietary
staple) from a high risk area for esophageal cancer in the African Repub-
lic of Transkei, compared with levels in a low risk area. However, these
mycotoxins, unlike aflatoxin, have not been shown to be carcinogenic.
Furthermore, results of the studies in Iran indicated that there were no
differences in aflatoxin (or nitrosamine) levels in foods in regions of
high and low risk for esophageal cancer.
A case-control study in Iran confirmed the inverse relationship be-
tween esophageal cancer and consumption of fresh fruit and cooked vege-
tables (Cook-Mozaffari, 1979; Cook-Mozaf f ari et_ al_. , 1979). The authors
concluded that the disease might be caused by opium use in combination
with diets low in fresh fruit and vegetables. In a case-control study of
white males in the United States, Mettlin t al. (1980) also found a
statistically significant inverse relationship, including a dose-response
gradient, between risk of esophageal cancer and frequency of consumption
of fruits and vegetables. Similar inverse associations were found for
indices of vitamin A and C intake, especially for vitamin C intake. In a
case-control study among Chinese in Singapore, de Jong e al . (1974)
17-3
found that a significant decrease in risk for esophageal cancer among
males was associated with consumption of bread, potatoes, and bananas.
They also found a direct association with consumption of very hot bever-
ages. Ziegler e aiL . (1981) examined the role of nutrition in the etiol-
ogy of esophageal cancer among blacks in the United States. They found
that nutrition in general was poorer among cases than controls, but they
identified no specific nutrient deficiency as responsible for the effect,
which appeared to be independent of ethanol consumption.
Warwick and Harington (1973) reported that large quantities of
grain, especially wheat and maize, are commonly consumed in most areas
with high risk for esophageal cancer. This observation was recently
extended by van Rensburg (1981), who examined esophageal cancer in-
cidence and relative frequencies with which dietary staples were con-
sumed in several populations, primarily in Africa and Asia. The low-
risk populations consumed millet, cassava, yams, or peanuts; the
high-risk populations consumed primarily wheat or corn, which provide
diets relatively deficient in zinc, magnesium, nicotinic acid, and
possibly riboflavin. He suggested that such nutritional deficiencies,
which may also occur in abusers of alcohol, might increase suscepti-
bility of the esophageal epithelium to neoplastic transformation. Thus,
it is possible that a common mechanism is involved in the causation of
esophageal cancer throughout the world.
In summary, a number of dietary factors appear to be associated with
the risk of esophageal cancer. An increased risk in some parts of the
world is associated with alcohol drinking, especially in combination with
cigarette smoke, high intakes of pickles and moldy foods possibly contain-
ing mycotoxins or N-nitroso compounds, trace mineral deficiencies, and
consumption of very hot beverages. Frequent consumption of fresh fruits
and vegetables appears to be associated with a lower risk for esophageal
cancer.
STOMACH CANCER
There is a high incidence rate of stomach cancer in Japan, in other
parts of Asia, and in South America; but in North America and Europe, the
incidence is low and is decreasing (Stukonis, 1978; Waterhouse et al
1976). In Japan, gastric cancer has been associated with chronic gastri-
tis (Imai e alU , 1971) and with the consumption of spiced and pickled
foods (Haenszel et al., 1976).
Surveys have shown that there is substantial variation in inci-
dence among different areas of Colombia (Cuello et_ ail. , 1976). These
variations have been correlated with different levels of nitrate in the
diet and drinking water (Correa e al_. , 1976; Tannenbaum et_ a!L. , 1979).
Broitman <et^ ad. (1981) studied iron-deficient patients in Medellin,
Colombia, who exhibited lesions that were precursors to gastric cancer.
They found that hypochlorhydria and achlorhydria associated with iron
17-4
deficiency permitted bacterial colonization of the stomach* Reduction
of dietary nitrate to nitrite, and subsequent endogenous synthesis of
N-nitroso compounds from nitrite, could thus be mediated by the gastric
flora. Ruddell et al. (1978) suggested a similar mechanism to explain
the increased risk for gastric cancer in patients with pernicious anemia.
An association between gastric cancer and high concentrations of
nitrate in drinking water was suggested by Hill et_ al^. (1973) s who ob-
served that mortality rates for stomach cancer were higher in Worksop,
England, where the water supply contained higher concentrations of
nitrate, than in nine control towns. However, Davies (1980) pointed
out that Worksop was a coal-mining town, and that stomach cancer has
been associated with coal-mining regions in Great Britain* Adjustment
for coal mining and socioeconomic status abolished the excess mortality
from stomach cancer in males in Worksop and reduced it markedly in
females*
In Chile, exposure of the general population to high concentrations
of nitrate in drinking water or in food appeared to be associated with
high rates of stomach cancer (Armijo and Coulsen, 1975; Zaldivar, 1977).
However , although nitrate levels were significantly higher in the urine
of schoolchildren from two areas of central Chile with high mortality
from stomach cancer than they were in the urine of schoolchildren from
a northern, low risk area, levels of nitrate were also significantly
higher in vegetables obtained from the low risk area (Armijo e_t al * ,
1981).
Dungal (1966) observed that large quantities of smoked foods (e.g.,
mutton and trout) were consumed in high incidence areas of Iceland and
that there was a lower incidence of stomach cancer in sailors than in
fanners in Iceland. He noted that sailors often stock food obtained at
foreign ports; thus, their diet contains a higher proportion of fresh
food. Choi et^ al_ (1971) showed that the mortality from gastric cancer
among Icelanders in Manitoba was twice as high as that among people born
in Manitoba. A dietary survey showed that the people born in Iceland
had consumed high levels of smoked and pickled foods.
**
Hakama and Saxen (1967) analyzed age- and sex-adjusted mortality
rates for stomach cancer in 16 countries. They found a strong corre-
lation (r = 0.75) with the per capita intake of cereals used for flour
during 1934-1938.
In the United States, counties with high mortality from stomach
cancer tend to be concentrated in Minnesota, Wisconsin, and the upper
peninsula of Michigan (Mason jet al. , 1975). Kriebel and Jowett (1979)
pointed out that although high rates in migrants from Northern Europe
may explain part of this increased mortality, the rates are dispropor-
tionately high. They suggested that native-born Americans have shared
the increased risk of the migrants, possibly by adopting the "high-risk"
diet of the foreign-born residents.
17-5
Over several generations, there has been a gradual decline in the
incidence of stomach cancer in Japanese migrants to the United States
(Kolonel et_ al_ , 1980) , suggesting that the risk factors for this cancer
exert their effect early in life*
Data from several countries indicate that there is a strong correla-
tion between mortality from gastric cancer and cerebrovascular disease.
Joossens and Geboers (1981) suggested that both diseases are related to
salt intake . However, the use of salt to preserve food is often accom-
panied by the use of nitrate for the same purpose (Weisburger et al. ,
1980)* Furthermore, Okamura and Matsuhisa (1965) found no correlaFion
between the salt content of salted fish and the death rate from gastric
cancer in Japan.
In a number of case-control studies, investigators have attempted
to define more specifically the role of diet and other factors in the
etiology of gastric cancer. Acheson and Doll (1964) and Wynder et al.
(1963) found no association with dietary factors. In another stucTy,
however, Meinsma (1964) observed that cases had eaten more bacon and
less citrus fruits (and, thus, less ascorbic acid) than had the con-
trols* Higginson (1966) found that cases had also consumed fried foods
more frequently, especially bacon drippings and animal fats used for
cooking. Hirayama (1967) reported that the daily consumption of milk
was less frequent and the daily use of salted foods was more frequent
among cases. Graham eMt al. (1972) observed that a low risk of gastric
cancer was associated with the consumption of raw lettuce, tomatoes,
carrots, coleslaw, and red cabbage and that there was a dose-response
relationship for these food items*
Haenszel et_ al* (1972) studied Japanese living in Hawaii. Migrants
(Issei) continued to display an increased risk in Hawaii, but the Nisei
offspring, who adhered to Western-style diets, did not. There were ele-
vated risks for both Issei and Nisei users of pickled vegetables and
dried/salted fish. Low risks were associated with the consumption of
several Western vegetables, many of which are eaten raw* Using a simi-
lar protocol, Haenszel ej^ jal* (1976) showed that farmers in Japan,
representing the lower socioeconomic class, had the highest risk for
gastric cancer. A lower risk was found for those whose diet included
more frequent use of lettuce and celery. Modan ejt^ al. (1974) reported
that starches were consumed more frequently by gastric cancer patients
than by controls.
Bjelke (1978) found an inverse relationship between stomach cancer
and consumption of vegetables and vitamin C, especially in younger pa-
tients and among women. He also reported preliminary findings from a
prospective study, showing a reduced risk for those with a high consump-
tion of vegetables in Norway, but not in Minnesota. The Norwegian study
also suggested that frequent use of salted fish may be associated with
a high risk of stomach cancer.
In a large cohort study conducted in Japan, Hirayama (1977) reported
that a protective effect against gastric cancer was associated with the
17-6
consumption of two glasses of milk daily and that there was an increased
risk in cigarette smokers. Nonsmokers who ate green or yellow vegetables
also had a lower risk of stomach cancer*
Weisburger and Raineri (1975) suggested that "gastric cancer in
humans may result from the in vivo nitrosation in the stomach of as yet
unknown substrates, with the production of alkylnitrosamides." They
postulated that exposure to reducing agents such as ascorbic acid may
interfere with the endogenous production of Jtf-nitroso compounds by the
reaction of dietary nitrite with amines or amides (Weisburger et al,
1980) . Such a mechanism could explain the protective effect of green
or yellow vegetables, raw lettuce, and other vitamin-C-containing
vegetables.
In summary, studies in migrants to the United States suggest that
gastric cancer is related in part to dietary factors that exert their
influence early in life. The factors increasing risk may include fre-
quent consumption of smoked food (which in some parts of the world
leads to increased exposure to polycyclic aromatic hydrocarbons) and
frequent ingestion of salt-pickled foods or foods containing nitrate and
nitrite (which may result in subsequent in vivo production of nitrosa-
mines) and other carcinogens produced in food by preservation treatments
and cooking. Protective factors may include consumption of milk, raw
green or yellow vegetables, especially lettuce, and other foods contain-
ing vitamin C.
COLON AND RECTAL CANCER
Haenszel (1961) reported that the rates of colon and rectal cancer
in migrants from Italy, Norway, Poland, and the Soviet Union more closely
resembled those in the host country (the United States) than those in
their country of origin, in contrast to the findings for stomach cancer.
Haenszel and Dawson (1965) observed that mortality for cancer of
the colon and rectum was higher in urban regions in the United States.
Urban-born people who migrate to rural areas acquire the lower mortality
of the rural areas; the reverse occurs for those who migrate from rural
to urban areas. Mortality is higher in the North than in the South for
long-term residents of these regions.
De Jong et al. (1972) found that in areas of high and intermediate
risk there is a decreasing incidence from the ascending colon to the
descending colon and a sharp increase at the sigmoid colon. Rectal
cancer rates are generally higher than those for the sigmoid. In low
incidence areas, there may be a low rate for sigmoid cancers.
Berg and Howell (1974) reviewed international mortality from cancer
of the bowel from 1952 to 1953 and from 1966 to 1967. The highest death
rates were reported in Scotland, but these rates were falling, as were
those for England and Wales. The rates for whites in the United States
17-7
appeared to be stable, but those for the Federal Republic of Germany,
Italy, and Japan were rising. The investigators interpreted differences
between colon and rectal cancer rates as indicating that, although much
of rectal cancer is caused by the same factors that cause colon cancer,
there is a second set of factors that affect rectal cancers alone.
Lee (1976) found that death rates from large bowel cancer in Japan
have risen rapidly since World War II and that colon cancer has increased
at a greater rate than rectal cancer. In Japan, each successive birth
cohort had an increased rate of colon cancer, whereas those in the United
States did not.
Haenszel a l. (1975) investigated the incidence of large-bowel
cancer in Cali, Colombia in relation to place of residence, by census
tract. They found that the upper socioeconomic classes were at higher
risk. Lynch t_ al^* (1975) also reported a greater frequency of colon
cancer in patients living in census tracts with higher average incomes.
Similarly, Teppo et^ al_. (1980) found a higher incidence of colon cancer
in higher socioeconomic areas of Finland.
Studies of the international incidence of and mortality from large
bowel cancer in relation to dietary variables strongly support an
association of colon cancer and, to a lesser extent, rectal cancer with
total dietary fat (Armstrong and Doll, 1975; Wynder, 1975). Irving and
Drasar (1973) failed to find a correlation between cancer of the colon
and the per capita intake of various fiber-containing foods. In studies
of mortality rates for colon cancer, Berg and Howell (1974) and Howell
(1975) reported that the highest correlations were found for per capita
meat intake, and that the highest was for beef. However, Enstrom (1975)
pointed out that the trends in per capita beef and fat intake in the
United States do not correlate with trends in incidence of and mortality
from colorectal cancer.
Jansson ot^ jJL. (1978) correlated the selenium concentration in water
samples from the eastern part of the United States with the incidence of
colorectal cancer. They found a strong, direct relationship between the
selenium content of water and colorectal cancer and observed that the
mean mortality rate increased with increasing levels of selenium in the
drinking water. Other studies, however, have shown an inverse correla-
tion between the intake of selenium and colon cancer (Schrauzer et al. ,
1977a,b; also see the section on selenium in Chapter 10).
Lui ^j^ ai. (1979) evaluated food disappearance data for 1954-1965 and
data on mortality from colon cancer for 1967-1973 from 20 industrialized
countries. They found that the per capita intakes of total fat, satu-
rated fat, monounsaturated fat, and cholesterol were directly correlated
and that fiber intake was inversely correlated with mortality from colon
cancer. The correlation of dietary cholesterol with colon cancer was
highly significant and remained so when they controlled for fat or fiber.
However, the correlations of fat or of fiber with colon cancer mortality
were no longer significant when they controlled for cholesterol.
1/-8
Bingham t^ aJU (1979) related the average intake of foods, nutrients,
and dietary fiber in Great Britain to the regional pattern of death from
colon and rectal cancer. They found that intakes of the pentosan frac-
tion of total dietary fiber and of vegetables other than potatoes were
inversely correlated with death rates for colon cancer.
The possible importance of dietary cholesterol (and/or dietary fat)
is supported by the correlations of mortality from colon cancer with
mortality from coronary heart disease in different countries (Rose et
al * 1974), correlations with large-bowel cancer among different social
classes in Cali, Colombia (Haenszel eit al . , 1975), and for cancer of the
colon and rectum together and individually within 34 health-planning
subdivisions in the Commonwealth of Massachusetts (Lipworth and Rice,
1979)* Stemmermann et_ al . (1979) noted the high rate of colon cancer
among Japanese who migrated to Hawaii and observed that myocardial
infarction, severe atherosclerosis, diverticulosis, and polyposis of
the colon also occurred more frequently in this population, compared
to Japanese living in Japan.
In studies of cancer incidence in Seventh-Day Advent ists, Phillips
and colleagues reported that a lacto-ovovegetarian diet had a protec-
tive effect against colon cancer (Phillips, 1975; Phillips t al . ,
1980a,b). The findings among Mormons in Utah (Lyon and Sorenson, 1978;
Lyon et^ajL. , 1976, 1980a,b) and in California (Enstrom, 1980) confirmed
that this group had a lower incidence of colon cancer than the U.S.
average, but were less clear with respect to the impact of dietary fac-
tors. f ln a preliminary dietary survey, Lyon and Sorenson (1978) found
little difference in meat, fat, and fiber intake by the population of
Utah and by the general U.S. population.
Malhotra (1977) suggested that the virtual absence of colon cancer
among Punjabis from northern India is due to their diet, which is rich
in roughage, cellulose, vegetable fiber, and short-chain fatty acids
contained in fermented milk products.
MacLennan ejt al. (1978) evaluated the diets consumed by adult men
from Kuopio, Finland and compared them with the diets consumed by a
similar sample from Copenhagen, Denmark, where the incidence of colon
cancer is 4 times higher. They found that the high incidence group
consumed more refined wheat breads, meats (especially pork), and beer,
but less potatoes and milk than did the low incidence group in Finland.
The estimated consumption of fat was similar, but the consumption of
fiber was higher in the low incidence group.
Reddy ej: al. (1978) studied the dietary patterns and fecal constit-
uents of a high risk group in New York and the low risk group in rural
Kuopio. The average daily intake of dietary fat and protein was the
same in the two groups, but a greater proportion of fat came from dairy
products in Kuopio and from meat in New York. The daily stool output
and fecal fiber excretion were also greater in Kuopio, where there was
a high dietary intake of cereal products rich in fiber.
17-9
These investigators found more mutagenic activity in the stools
from New York subjects who were not Seventh-Day Adventists than in the
stools obtained from subjects in Kuopio, who had a similar fat but a
higher fiber intake (Reddy et_ al. , 1980). However, they found no mu-
tagenic activity in the stools~T r rom vegetarian Seventh-Day Adventist
volunteers from New York, who had a lower average fat intake than the
other two groups, but an intermediate level of fiber intake*
A number of case-control studies have been conducted to examine the
relationship between diet and cancer of the large bowel. Wynder and
Shigematsu (1967) could not identify environmental factors that differed
significantly between cases and controls* A study of Japanese patients
with bowel cancer and hospital controls in Hawaii indicated that there
was a higher risk for persons who regularly ate Western-style meals
(Haenszel et_ al/ , 1973). Control for beef produced the largest downward
displacement in estimated risks for other dietary variables. In Japan,
a study conducted with similar methodology did not replicate these find-
ings (Haenszel e al. , 1980); however, reduced risk was associated with
consumption of cabbage.
Modan et^ al. (1975) found that fiber-containing foods were con-
sumed less frequently by cases of colon cancer than by controls, but
there were no differences for cases with rectal cancer. They also
observed no differences in consumption of fat-containing foods by
either cancer group or the controls.
Parallel studies in Norway and Minnesota indicated that there was
a slightly lower consumption of cereal products, milk, and coffee by
colorectal cancer cases, compared to controls, and several vegetables
were eaten less frequently by the cases (Bjelke, 1978). The cases also
had lower indices for consumption of vitamin A and crude fiber, both of
which are associated with vegetable intake. In the United States,
Phillips (1975) found that consumption of beef, lamb, and fish, and the
heavy use of dairy products other than milk and other high-fat foods,
were directly associated with the risk of colon cancer, and that there
was a slight inverse association with the consumption of milk, vegeta-
ble protein products, and green leafy vegetables*
Dales e al . (1979) reported that foods with at least 0.5% fiber
content were consumed less frequently by colon cancer cases than by
the controls, and that there was a consistent dose-response relation-
ship. Cases tended to have eaten foods with at least 5% saturated fat
more often than controls. Significantly more cases than controls re-
ported a high saturated fat, low fiber food consumption pattern.
Graham et al. (1978) reported that a decreased risk of colon cancer
was associatd"~with frequent ingestion of vegetables, especially cabbage,
brussels sprouts, and broccoli. Decreased risk of rectal cancer was
associated only with frequent ingestion of raw vegetables and cabbage.
17-10
However, Martinez e^ al. (1979) reported that cases had consumed signif-
icantly higher quanFitTes of meats, cereals, total fats, total residue,
and fiber .
Jain et al. (1980) observed that an increased risk of both colon and
rectal cancer was associated with elevated consumption of calories, total
fat, total protein, saturated fat, oleic acid, and cholesterol, but that
there was no association with consumption of crude fiber, vitamin C, and
linoleic acid. The highest risk was found for saturated fat consumption,
and there was evidence of a dose-response relationship.
The only cohort studies that have yet provided data on dietary vari-
ables are the ongoing parallel studies in Norway and Minnesota (Bjelke,
1978). These studies indicate that there is a reduced risk of colorectal
cancer in the Minnesota subjects who have a high index of vegetable con-
sumption. No such effect has been observed in Norway, but the number of
cases in that country is small.
Most information on the association between colon cancer and choles-
terol levels has been derived from epidemiological studies and interven-
tion trials to determine risk for cardiovascular disease. The findings
have been conflicting, and it is not certain whether reported increases
In risk of cancer (especially colon cancer) at low serum cholesterol
levels reflect a causal association (Feinleib, 1981; Lilienfeld, 1981).
Rectal cancer has been associated with intake of beer in some stud-
ies (Breslow and Enstrom 1974; Dean et_ al . , 1979; Enstrom, 1977; Stocks,
1957), but not In all studies (Jensen, 1979; Schmidt and Popham, 1981).
McMichael et a 1 . (1979) suggested that there is a better correlation be-
tween trends In mortality from rectal cancer and changes in beer intake
than has been found for saturated fat.
Wynder and Shigematsu (1967) showed that the proportion of beer
drinkers among male colorectal cancer patients was significantly higher
than in one control group, but not in a second control group. In a
prospective study conducted by Bjelke (1973), there was a dose-response
relationship between the risk of colorectal cancer and the frequency of
beer and liquor consumption. The gradient was steeper for beer consump-
tion. Conversely, case-control studies of intestinal cancer in Finland,
Kansas, and Norway (Bjelke, 1971, 1973; Higginson, 1966; Pernu, 1960)
indicated that there was no significant relationship with beer drinking.
Vitale et al.. (1981) reported a correlation coefficient of 0.78 between
alcohol consumed as beer and colon cancer in 20 countries. There were
poor correlations for colon cancer and the intake of total ethanol,
distilled spirits, or wine.
In summary, three hypotheses appear to be supported by data of vari-
ous strengths obtained from epidemiological studies of both colon and
17-11
and rectal cancer: (1) a causal association with total, and perhaps satu-
rated, fat; (2) a protective effect of dietary fiber; and (3) a protective
effect of cruciferous vegetables. The diverse results concerning the im-
portance of fat and fiber may be partly due to differences in the degrees
of precision in the dietary methodology used in the various studies. The
possible role of alcohol in the induction of rectal cancer requires fur-
ther study.
LIVER CANCER
Primary liver cancer is relatively uncommon in the United States and
most Western countries, but it is a major form of cancer in sub-Saharan
Africa and Southeast Asia. Several different dietary agents have been
reported as possible hepatic carcinogens, including alcohol, aflatoxin,
safrole, pyrrolizidine alkaloids, and cycasin (Anthony, 1977).
Oettle (1965) suggested that the geographic distribution of liver
cancer in Africa could be explained by differing levels of exposure to
aflatoxin in the diet. In a number of studies, aflatoxin contamination
of foodstuffs has been correlated with liver cancer incidence and mor-
tality by geographic area or for different population groups in Africa
(Alpert e al^ , 1971; Keen and Martin, 1971; Peers and Linsell, 1973;
Peers et^ al . , 1976; van Rensburg ejt aJL . , 1974). Similar correlations
have been found in Thailand, China, and Taiwan, which also have high
rates of liver cancer (Armstrong, 1980; Shank et_ aJL. , 1972a,b; Tung and
Ling, 1968; Wogan, 1975). There is a strong correlation between the
estimated levels of aflatoxin ingestion and liver cancer rates in these
various studies, and no populations with documented high levels of afla-
toxin ingestion have low rates of liver cancer (Linsell and Peers, 1977).
Numerous reports (e.g., Chien al* , 1981) have also documented a
high correlation between primary liver cancer and exposure to hepatitis
B viral infection, which has a worldwide distribution similar to that of
aflatoxin. Many investigators believe that although primary liver cancer
could be initiated by aflatoxin, there is a higher probability that liver
cancer develops in individuals exposed to the hepatitis B virus.
In Guam and Okinawa, which have high rates of liver cancer, the
Ingest/ion of cycasin (a toxic substance contained in cycad nuts) has
been proposed as an etiologlc factor. However, in a descriptive study
conducted in the Miyako Islands of Okinawa, investigators found no
correlation between mortality from hepatoma and the ingestion of cycad
nuts (Hirono <et_ al. , 1970).
Alcohol is the main dietary factor that has been suggested as an
etiologlc agent for liver cancer in Western, low-risk countries, al-
though Armstrong and Doll (1975) reported a weak correlation between
liver cancer incidence (but not mortality) and per capita intake of
17-12
potatoes in more than 20 countries . Interest In alcohol as a causal
factor for primary liver cancer was generated by reports of hepatomas
occurring at increased rates in cirrhotic patients with histories
of heavy alcohol use and by other reports of high rates of alcoholic
cirrhosis in hepatoma patients (Lee, 1966; Purtilo and Gottlieb* 1973).
However, the cirrhosis usually associated with liver cancer is the
macronodular form, which is characteristically associated with hepatitis
B viral infection (Anthony, 1977) . Furthermore, ethanol itself has not
been shown to be carcinogenic in animals (Vitale and Gottlieb, 1975)*
Most descriptive epldemlological data do not support the association
between alcohol intake and risk of liver cancer* Esophageal cancer has
been linked to alcohol consumption; however, the incidence rates for
esophageal cancer in various countries have been significantly correlated
with liver cancer in men, but not in women (Miller, 1981)* Despite dif-
ferences in alcohol consumption between Mormons and non-Mormons in Utah
and between Issei and Nisei Japanese in Hawaii, both groups in Utah and
both in Hawaii have similar Incidence rates for liver cancer (Kolonel et
al., 1980; Lyon e al . , 1976, 1980a,b) There is also no significant
correlation between ethnic patterns of liver cancer Incidence in Hawaii
and alcohol consumption (Hinds e al_* , 1980).
There have been few analytical studies of the relationship between
alcohol and liver cancer. In a proportional mortality analysis, Monson
and Lyon (1975) found no increase in deaths from liver cancer among
alcoholics admitted to mental hospitals in Massachusetts. Conversely,
Hakulinen et al* (1974) found that liver cancer cases in two alcohol
abuser populations in Finland exceeded the number expected, based on
data in the Finnish Cancer Registry. In a retrospective cohort study of
male alcoholics in Ontario, Canada, Schmidt and Popham (1981) observed
that liver cancer deaths were 2 times higher than expected, based on the
general population of Ontario, but the numbers were small and the differ-
ence was not statistically significant*
In summary, high intake of foods contaminated with aflatoxin Is asso-
ciated with liver cancer in high incidence areas of the world, i.e., Asia
and Africa. Chronic infection with hepatitis B virus, which has the same
geographic distribution as aflatoxin contamination, has been proposed as
a primary etiologlc factor in liver cancer. The evidence that excessive
alcohol consumption may indirectly contribute to the development of some
types of liver cancer is extremely tenuous.
PANCREATIC CANCER
The per capita intake of several foods has been associated with pan-
creatic cancer Incidence and mortality in a number of international
studies. Analyses of mortality data have produced direct associations
with intake of fats and oils, sugar, animal protein, eggs, milk, and
coffee (Armstrong and Doll, 1975; Lea, 1967; Stocks, 1970; Wynder et al.,
17-13
1973). From incidence data, there was a direct correlation only with
per capita intake of eggs (Armstrong and Doll, 1975). In a correlation
analysis by county in the United States, Blot e al. . (1978) found that
there was a direct association with alcohol intake. In contrast, Hinds
et_ al. (1980) reported that pancreatic cancer incidence in five ethnic
groups in Hawaii correlated directly with beer consumption, after con-
trolling for cigarette smoking and consumption of other types of alco-
holic beverages. This finding was in agreement with the observation of
Kolonel et al. (1980) that pancreatic cancer Incidence rates are the same
for migrant and native-born Japanese groups in Hawaii, which have similar
rates for beer consumption but not for total alcohol consumption. Lyon
t. !_ (1980a,b) observed that non-Mormons in Utah have higher incidence
rates of pancreatic cancer than do Mormons, who drink less alcohol, tea,
and coffee-
Reports of several case-control studies have indicated an associa-
tion between diet and pancreatic cancer. Based on data obtained from
relatives of cases and controls, who responded to a mailed questionnaire,
Burch and Ansari (1968) found a direct association between pancreatic
cancer and chronic alcoholism. Using a similar design, Ishii et_ al .
(1968) found direct associations with alcohol and meat consumption (men
only) and an inverse association with vegetable intake. Lin and Kessler
(1981) reported that the consumption of wine by female cases was greater
than that of controls, a finding not observed in the males. In contrast,
Wynder e al. (1973) and MacMahon et^ al. (1981) found no association
between pancreatic cancer and alcohol consumption. Wynder et_ al . (1973)
did find a direct association with early-onset diabetes in women, and
MacMahon et al. (1981) reported a direct association with coffee con-
sumption and a dose-response gradient for women only. Lin and Kessler
(1981) also noted a greater consumption of decaffeinated coffee by cases
than by controls.
Two cohort studies have reproduced the association of pancreatic
cancer with diabetes in women, which was observed in the case-control
study of Wynder et_ al. (1973) and in the correlational analyses of Blot
et^ aLL. (1978). After studying a cohort of diabetics for 29 years,
Kessler (1970) found excess deaths from pancreatic cancer, despite fewer
overall cancer deaths than expected. Armstrong ^ l/ (1976b) also fol-
lowed a cohort of diabetics and found a slight Increase in mortality from
pancreatic cancer (although not statistically significant) and an overall
decrease in mortality from all cancers. Hirayama (1977) reported a rela-
tive risk of 2.5 for daily meat consumption and pancreatic cancer in a
cohort study conducted in Japan, thereby reproducing a similar finding in
the case-control study of Ishii eit ad (1968).
In summary, there is limited evidence that certain dietary factors
(e.g., the intake of alcohol, coffee, and meat) are associated with an
elevated risk for cancer of the pancreas.
17-14
GALLBLADDER CANCER
There is a high incidence of gallbladder cancer in Latin America,
Japan, and Southeast Asia for both sexes but it is higher for females
than for males (Waterhouse et^ .1. , 1976). Cancer at this site is rela-
tively uncommon among blacks and whites in the United States, but occurs
more frequently among North American Indians and Mexican-American females.
It has also been associated with gallstones, obesity, and type IV hyper-
lipoproteinemia (Fraumeni, 1975a). Among the dietary risk factors that
have been postulated are both high calorie and high fat diets. However,
the uniformly poor correlation of gallbladder cancer with other cancers
associated with high fat diets appears to militate against high fat diets
as a causal factor. No case-control study of dietary factors and cancer
of this site has been reported.
The evidence for a dietary etiology of this cancer is therefore in-
direct and rather weak at this time, other than an association with obes-
ity and, therefore, possibly an excess of calories.
LUNG CANCER
Lung cancer is the most prevalent cancer in men in most technically
advanced countries, and it is rapidly approaching this level in women
(Miller, 1980; Waterhouse et^ al . , 1976). The most important causal fac-
tor is cigarette smoking (Surgeon General, 1979). Occupational exposures
contribute substantially to the incidence in males (Fraumeni, 1975b). In
women, cigarette smoking probably accounts for more than one-half of the
cases (Surgeon General, 1980).
Bjelke (1975) conducted a prospective study of 8,278 Norwegian men
who responded to a mailed questionnaire designed to determine the associ-
ation between vitamin A intake and lung cancer. As a result of observa-
tions made during a 5-year follow-up of this group, Bjelke was one of the
first to suggest a relationship between vitamin A intake and cancer at
this site. He found that the relative- risk for lung cancer was 2.5 times
higher for current and former smokers in the low vitamin A intake group
than for those in the high intake group.
Subsequently, a number of other investigators studied this associa-
tion. Basu ejt al. (1976) and Sakula (1976) found that levels of vitamin
A in the plasma of bronchial carcinoma patients were lower than those in
the serum of controls. MacLennan et^ al. (1977) studied the relationship
between consumption of dark green, leafy vegetables rich in vitamin A
precursors and the risk of lung cancer in Chinese female cases and con-
trols in Singapore. They found a relative risk of 2.2 for low indices
of vegetable intake. Smith and Jick (1978) assessed the frequency with
which preparations containing vitamin A were used by newly diagnosed lung
cancer patients and patients with nonmalignant conditions. They found an
inverse association among men, but not among women. Mettlin et al. (1979)
17-15
found a dose-response relationship for lung cancer up to risk ratios
of 2.4 for heavy smoking men with a low index of vitamin A consumption.
Shekelle _et^ al_ . (1981) studied a prospective cohort of 1,954 men in
Chicago. After 19 years of followup, they found a significant inverse
association between lung cancer incidence and the intake of carotene,
after adjustment for cigarette smoking. In contrast, lung cancer was
not significantly associated with the intake of preformed vitamin A.
In summary, there is evidence that low dietary levels of foods con-
taining vitamin A and/or vitamin A precursors (e.g., g-carotene) are
associated with increased risk of lung cancer, especially among heavy
smokers. Because the indices of vitamin A Intake in these studies were
derived from foods that also contain other natural inhibitors of carcino-
genesis, it is also possible that dietary constituents other than pre-
formed vitamin A or carotene are the relevant risk-reducing factors.
BLADDER CANCER
Most of the epidemiological literature on the association between
diet and bladder cancer pertains to coffee and nonnutritive sweeteners.
In both correlation and case-control studies, direct associations have
been found between coffee consumption and bladder cancer (C. T. Miller et
al., 1978; Simon e a^. , 1975; Wynder and Goldsmith, 1977); however, in
most of the case-control studies, investigators failed to find a dose-
response gradient. In other epidemiological studies, no association at
all was found between coffee consumption and bladder cancer. These
studies are reviewed in Chapter 12.
There are similarly conflicting findings in the epidemiological
literature on nonnutritive sweetener use and bladder cancer. Both corre-
lational data and observations in studies of diabetics have failed to
implicate nonnutritive sweetener use in the etiology of bladder cancer
(Armstrong et^ aJ. , 1976b; Kessler, 1970). In some case-control studies,
investigators found an association; in others, they did not. With the
exception of a study by Howe et_ al . (1977), direct associations were
observed only in very select, low-risk subgroups, e.g., nonsmoking women
without occupational exposure to bladder carcinogens (Hoover and Strasser,
1980). These studies are discussed in detail in Chapter 14.
The epidemiological literature pertaining to the association of other
dietary exposures and bladder cancer is much more limited. In an analysis
based on international data, Armstrong and Doll (1975) found a direct
association of bladder cancer mortality, but not incidence, with per
capita intake of fats and oils, particularly in women. In another cor-
17-16
relation study , based on data by state in the United States , there was a
direct association between beer intake and bladder cancer mortality in
men (Breslow and Enstrom, 1974).
In a report of a case-control study , Mettlin and Graham (1979) ob-
served that there was an inverse association between bladder cancer and
an index of "vitamin A" intake as well as with consumption of carrots and
milk. In another case-control study , Howe aJL (1980) found a direct
association between bladder cancer and consumption of coffee and no
association with consumption of tea, alcohol, soft drinks* fiddlehead
greens (related to bracken fern, which is a bladder carcinogen in cattle),
or meats preserved with nitrite (such as hams and sausages). Nitrosa-
mines (presumably formed from precursors of dietary origin) have been
found in the urine of patients with urinary tract infections (Hicks et
al. , 1977; Radomski t al. , 1978).
In summary, bladder cancer has frequently been associated with cof-
fee consumption, although the relationship does not appear to be causal.
The use of nonnutritive sweeteners (primarily saccharin) does not appear
to be a significant risk factor, except perhaps in some very select low
risk groups. A possible inverse association with an index of "vitamin A"
intake has been reported in one study.
RENAL CANCER
The epidemiological data on dietary factors related to renal cancer
are meager. International incidence and mortality data have shown cor-
relations of renal cancer with per capita intake of coffee, milk, meat,
total fat, and animal protein (Armstrong and Doll, 1975; Shennan, 1973).
In a correlation study of ethnic-specific incidence rates for renal
cancer with corresponding intakes of alcohol based on representative
interview data, Hinds <^t aJ . (1980) found a direct association for beer
consumption, but not for the consumption of wine or hard liquor. A
similar direct correlation for beer intake and renal cancer was reported
by Breslow and Enstrom (1974), who compared mortality data and per capi-
ta alcohol intake by state in the United States.
These associations have not been reproduced in case-control studies
of renal cancer. In a case-control study by Wynder ej^ aJL, (1974), there
were no differences for coffee drinking or alcohol consumption; however,
they did report that the relative weight of female (but not male) cases 2
years before the onset of illness was greater than that of the con-
trols. Armstrong e al . (1976a) also found no direct associations with
the frequency of intake of coffee, tea, alcohol, chocolate, or the major
food sources of animal protein. Kolonel (1976) observed a direct asso-
ciation between renal cancer and combined exposure to cadmium from three
sources: diet, cigarette smoking, and occupational setting.
17-17
BREAST CANCER
Breast cancer is the commonest cause of death from cancer among
women In North America. In the United States, it Is the cause of more
deaths than any other cause among women between the ages of 40 and 44.
It Is known that cancer at this site is associated with hormonal activi-
ty, but diet has also been suspected as a major cause (MacMahon et al.,
1973).
Several types of studies have provided evidence supporting the
importance of dietary factors in breast cancer: descriptive epldemlo-
logical studies, correlation studies, evaluations of nutrition-mediated
risk factors, and case-control studies. Additional evidence for an
association has been provided in reports of studies in laboratory
animals, which are discussed in Chapter 5.
The evidence from descriptive epideinlologlcal studies suggests that
cultural factors or lifestyle, especially diet, are influential In the
etiology of breast cancer* For example, the incidence of breast cancer
among premenopausal Japanese-American women living in California is now
almost as high as that for Caucasian women (Dunn, 1977); whereas the
incidence of cancer among them was similar to that in Japan when they
first migrated. Moolgavkar et_ aJL . (1980) have shown that changes In
cancer incidence for certain populations can be related to changes in
lifestyle of successive birth cohorts.
The second type of evidence has been provided by studies correlating
breast cancer Incidence and mortality with per capita intake of total
fat and other nutrients in different countries (Armstrong and Doll,
1975; Carroll, 1975; Drasar and Irving, 1973; Hems, 1978; Knox, 1977),
Including Japan (Hirayama, 1977) and the United States (Enig et al.,
1978; Kolonel e al . , 1981). Gaskill et_ al. (1979) found a direct cor-
relation between breast cancer mortality and intake of milk, table fats,
beef, calories, protein, and fat, and an inverse correlation with intake
of eggs. Milk and egg intake remained significantly associated (directly
and inversely, respectively) with breast cancer when the Investigators
controlled for age at first marriage.
The third type of evidence is derived from evaluating certain, prob-
ably nutrition-mediated, factors that affect the risk of breast cancer.
These factors include weight, height, body mass (which is dependent on
height and weight) (de Waard 1975; de Waard and Baanders-van Halewijn,
1974; de Waard et al., 1977), and age at menarche (MacMahon et al . ,
1973; Miller, 1978). Women who experienced menarche at an early age,
especially before the age of 12, were at higher risk. Evidence that
body weight and food intake are related to early onset of estrus in rats
(Frlsch et_ al_. , 1975) supports the hypothesis that the rat's body must
contain a minimum amount of fat for estrus to occur. This also appears
17-18
to be essential for menarche in women (Frlsch and McArthur, 1974); how-
ever, not all studies of these factors have confirmed these findings
(Miller, 1981), perhaps reflecting the overriding importance of other
variables more directly related to nutrition.
Gray et_ al (1979) evaluated the effect of per capita intake of
total fat"~and animal protein on international incidence and mortality
rates for breast cancer, while controlling for height, weight, and age
at menarche. They found that a significant effect of the dietary vari-
ables persisted after controlling for the other factors.
Case-control or cohort studies should provide the most conclusive
evidence. "Thus far, no cohort studies have been reported. Of the three
case-control studies that have been reported, one involved 77 breast
cancer cases and 77 controls (Phillips, 1975). In this study, five
categories of foods were associated with breast cancer: fried foods,
fried potatoes, hard fat used for frying, dairy products (except milk),
and white bread. The relative risks ranged from 1.6 to 2.6.
In the case-control study of 400 cases and 400 neighborhood controls
reported by A. B. Miller et_ aJU (1978), the mean nutrient consumption
was estimated from dietary histories for six nutrients. In the premeno-
pausal group, the strongest association was found for total fat con-
sumption. There were weaker associations for saturated fat and choles-
terol. When the effect of each nutrient was controlled for the effect
of the others, the association for total fat consumption became stronger,
whereas the association for saturated fat and cholesterol diminished.
In the postmenopausal group, the only consistent finding was an associa-
tion for total fat consumption. The risk ratios were low (1.6 for total
fat In premenopausal women and 1.5 for postmenopausal women), and there
was no evidence of a dose-response relationship.
In the third case-control study, which involved 577 cases and 826
controls, Lubin e al. (1981) found that relative risk Increased signif-
icantly with more frequent consumption of beef and other red meat, pork,
and sweet desserts. Analysis of computed mean daily nutrient intake
supported a link between breast cancer and consumption of animal fat and
protein.
Nomura e SLU (1978) compared the diet of Japanese men whose wives
had developed^ txreast cancer with the diets of other Japanese men who had
participated in the Japan-Hawaii Cancer Study. They assumed that the
diets of the husbands and wives were similar. Their results Indicated
that the husbands of the cases consumed more beef or other meat, butter/
margarine/cheese, corn, and wieners, and that they ate less Japanese
foods than did the control group.
In summary, information derived from a number of different types of
studies support the association of diet, especially high fat diets, with
17-19
breast cancer. The association is weak, if examined for individuals
rather than for populations. One explanation for this may be that the
effect of diet takes place early in life and is indirect , possibly in-
fluencing cancer risk by its effects on hormones (Miller and Bulbrook,
1980).
ENDQMETRIAL CANCER
Endometrial (uterine) cancer has been correlated with other cancers
that are associated with dietary factors (e.g., cancers of the breast,
ovary, colon, and rectum) (Miller, 1981) and has been associated with
higher socioeconomic status. In correlation studies, it has been asso-
ciated primarily with high per capita intake of total fat (Armstrong and
Doll, 1975).
Two indirect indicators of the effect of nutrition have been evalu-
ated in case-control studies. In two such studies, an association was
found with obesity (Elwood et_ _aJU , 1977; Wynder e al. , 1966), although
the excess risk appeared to be restricted to the most obese group. In
one of these studies, Elwood ejt^ JL!. (1977) observed no association with
height. Thus far, there have been no case-control studies directly
comparing the effects of diet on cases of endometrial cancer and con-
trols.
In summary, the evidence for an association between endometrial
cancer and diet is indirect. It is derived mainly from the similarity
between the occurrence of this disease and cancer of the breast and
colon. The recent dramatic increases in the incidence of endometrial
cancer have been clearly related to the use of exogenous estrogens at
the time of menopause (Jick e al_. , 1980); they do not appear to be
related to any factor in the diet.
OVARIAN CANCER
The evidence associating dietary factors, especially high fat diets,
and ovarian cancer is largely indirect. It includes both international
and national correlations between incidence of and mortality from ovari-
an cancer and other diet-associated cancers, especially cancers of the
breast and colon (Miller, 1981), and the correlation of dietary varia-
bles, especially per capita intake of total fat, with incidence of and
mortality from ovarian cancer (Armstrong and Doll, 1975; Lingeman, 1974) ,
In one case-control study, Annegers e al_. (1979) observed that
obesity is not a risk factor for ovarian cancer, and in another,
Hildreth e alU (1981) found no effect of height or weight. No case-
control studTes evaluating dietary variables directly have yet been
reported. There is, however, a greater than expected risk of second
17-20
primary cancers of the corpus uteri , colon, and breast in patients with
ovarian cancer (Reimer et_ al , 1978)- This supports the hypothesis that
there are common etiological factors for these sites*
PROSTATE CANCER
Several investigators have correlated dietary intake data with inci-
dence of and mortality from prostate cancer- Stocks (1970) reported a
direct correlation of prostate cancer mortality with per capita coffee
intake in 20 countries. In a similar analysis, Armstrong and Doll
(1975) found a significant direct correlation of prostate cancer mor-
tality, but not incidence, with the per capita intake of total fat and
the intake of fats and oils. They noted a high intercorrelation of
coffee and fat consumption in their data, which they believed could
explain the association with coffee drinking reported by Stocks. Howell
(1974) found a high direct correlation between mortality from prostate
cancer in 41 countries and per capita intake of fats, milk, and meats
(especially beef), and an inverse correlation with intake of rice.
Blair and Fraumeni (1978) observed that U.S. counties with the highest
prostate cancer mortality among whites were those with greater per capi-
ta intake of high fat foods (e.g., beef products, milk products, fats
and oils, pork, and eggs). A correlational analysis based on dietary
data obtained from individual interviews in Hawaii indicated that there
was a significant association between incidence of prostate cancer in
five ethnic groups and the consumption of animal fat and protein
(Kolonel et^ al^ , 1981). Furthermore, it has been observed that both
prostate cancer incidence and fat intake are higher among Japanese in
Hawaii than in Japan (Kato e al. , 1973; Waterhouse et^ ad. , 1976).
These observations are further supported by international incidence
and mortality data indicating that there are significant correlations of
prostate cancer with cancers of other sites associated with diet, in-
cluding cancer of the breast, corpus uteri, and colon (Berg, 1975;
Howell, 1974; Wynder ej^ al. , 1971). However, there are important excep-
tions. For example, the Mormons in Utah have high prostate but low
breast cancer incidence rates, and the native Hawaiians have low pros-
tate but high breast cancer incidence rates (Kolonel, 1980; Lyon et al. ,
1976).
There have been few case-control studies of prostate cancer and
diet. Rotkin (1977), in an interim report, observed that high fat foods
(including beef, pork, eggs, cheeses, milk, creams, and butter/margarine)
were consumed more frequently by cases than by matched hospital controls.
Schuman ejt l. (1982) reproduced this finding in a study conducted in
Minnesota. They also reported that the consumption of foods rich in
vitamin A (e.g., liver) or its precursors (e.g., carrots) were lower
for cases than for controls. Kolonel and Wlnkelstein (1977) found no
difference between cases and controls in exposure to cadmium from
17-21
dietary sources* This lack of association is interesting in light of
reports indicating that there are direct associations between prostate
cancer and exposure to cadmium in occupational groups (Adams e t a 1 ,
1969; Kipling and Waterhouse, 1967; Lemen ejt al . , 1976; Potts~1965),
and the knowledge that diet is the main source of exposure to cadmium
for the general population (Friberg et_ aJ. , 1974)
After a 10-year follow-up of a cohort of 122,261 Japanese men aged
40 years and older, Hirayama (1979) found an inverse association between
daily intake of green or yellow vegetables and mortality from prostate
cancer. Hirayama (1977) also reported that prostate cancer occurred at
a lower rate among vegetarian men in this cohort.
In summary, the incidence of prostate cancer is correlated with
other cancers associated with diet, e.g., breast cancer. There is good
evidence that an increased risk of prostate cancer is associated with
certain dietary factors, especially the intake of high fat and high
protein foods, which usually occur together in the diet. There is some
evidence that foods rich in vitamin A or its precursors and vegetarian
diets are associated with a lower risk.
17-22
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CHAPTER 18
ASSESSMENT OF RISK TO HUMAN HEALTH
The literature on risk assessment has expanded rapidly in recent
years* Some of the most comprehensive reports have been prepared by
committees of the National Academy of Sciences (1977, 1980a,b). This
chapter is only Intended to supplement that literature with primary ref-
erence to risk analysis of the effects of diet, particularly nutrients,
on the process of carcinogenesis. In this context, risk is defined as
the probability that an individual will develop cancer within a given
time. Such risk can be estimated by examining retrospective data.
To determine dietary and nutritional effects on cancer, it is useful
to relate risk analysis to the basic concepts of carcinogenesis. That
is, chemically induced carcinogenesis may Include (a) an initiation
phase, when chemicals or other agents possessing genotoxlc activity
Interact with the genome of somatic cells, and (b) a modification phase,
when a variety of events modify that process either simultaneously with,
or subsequent to, the initiation phase.
Initiators of carcinogenesis are generally mutagenic in one or more
systems (McCann e aJU , 1975; Purchase e al_. , 1978; Sugimura et al.
1976) and form covalent adducts with DNA and other cellular macromole-
cules, usually after enzymatic metabolism (Boyland and Levi, 1935) to
chemically reactive metabolites (Magee et aJL. , 1975; Miller, 1970). If
such adducts or other interactions between DNA sites are not removed or
repaired, and If the cell, through replication, transmits this molecular
aberration to future cell generations, then the initiating event is con-
sidered to be irreversible.
In contrast to compounds that act as Initiators, many other compounds
may modify either the Initiating events per se, or the subsequent multi-
staged events responsible for the progression of the Initiated cell to
the fully developed neoplastic cell (Slaga, 1980). A wide variety of
chemicals can modify later stages of carcinogenesis. Many of them act
exclusively as modifiers; others are also initiators (complete carcino-
gens).
The process of carcinogenesis may be modified through a great many
diverse mechanisms, which can involve the Intervention of several physio-
logical/biochemical systems, including changes in the function of the
enzymes, hormones, Immune response, membrane transport and communication
activities, etc. Some modifiers have positive effects (i.e., they are
promoters or cocarcinogens), whereas others have negative effects (i.e.,
18-2
they are inhibitors of initiation, antipromoters, or anticocarcinogens)
on the progression of the initiated cell to the tumorigenic state* In
contrast to initiation, the progress of positive modification (promotion)
appears to be more reversible (Doll and Hill, 1964; Roe and Clack, 1963).
This distinction between initiation and modification is necessary for
an understanding of the literature on risk analysis. Most such litera-
ture assumes that carcinogenic substances act as initiators. Models
developed for initiation, e.g., those for threshold response, additivity
vs. nonadditivity of toxic response, dose- response kinetics, and extent
of exposure ("hitness"), do not necessarily apply to assessment of risk
due to tumor modifiers. For example, one of the most straightforward
differences is the direct correlation between dose and tumor response for
initiators versus the inverse correlation between the tumor response and
the dose of certain modifiers such as several nutrients and certain
antioxidants.
Food may contain both initiators and modifiers of carcinogenesis (see
Chapters 12 and 14). The great diversity of initiators to which humans
are exposed is suggested by the wide variety of mutagens with a broad
range of potencies present in the food we eat and the excreta produced
(Bruce e.t_ l . , 1977; Sugimura, 1979). There will always be an ample
supply of modifiers in food, including a variety of nonnutritive sub-
stances and most, if not all, nutrients (when consumed in amounts that
either exceed or are less than those required for optimum nutrition).
These modifiers may affect carcinogenesis by influencing hormone status
(Alberti, 1980), immune response (Axelrod, 1980; Gross and Newberne,
1980), and the activity of carcinogen-metabolizing enzymes (Campbell,
1979; Conney, 1967).
INITIATORS OF CARCINQ GENES IS
In general, two procedures may be used to estimate acceptable levels
of risk for toxic compounds. One method estimates the acceptable daily
intake (ADI); the second is the "risk estimate" approach (National
Academy of Sciences, 1980a).
The ADI is an arbitrary estimate that "is not an estimate of risk nor
a guarantee of absolute safety" (National Academy of Sciences, 1980a).
It has been widely used for noncarcinogenic toxic chemicals and is based
on empirical data pertaining to acute toxicity. This procedure was modi-
fied by the Safe Drinking Water Committee to estimate acceptable daily
intake for contaminants in drinking water because of the paucity of data
for these compounds (National Academy of Sciences, 1977). To establish
an ADI, the highest experimental dose that produces no observable effects
is decreased by an "uncertainty factor" or "safety factor" (ranging from
18-3
10 to 5,000) in order to minimize the probability of harm to the more
sensitive members of the general population. A commonly used safety
factor for chronic toxicity tests is 100, which assumes a factor of 10 to
allow for variability of individual responses within the test species and
a second factor of 10 for the assumed differences in response between the
test species and humans (Lehman and Fitzhugh, 1954). Although the 100-
fold safety factor has been widely used to evaluate food additives and
other chemicals (World Health Organization, 1958, 1972), there are no
empirical data to support this specific factor. In general, the greater
the uncertainty in the experimental data, the larger the safety factor
(National Academy of Sciences, 1977). The ADI method is unacceptable for
estimating risk for initiators because there is a great variation among
species in susceptibility to carcinogens, and because of the serious
consequences for regulatory action if the estimates are misleading
(National Academy of Sciences, 1980a).
The more appropriate approach for estimating risk for initiators of
carcinogenesis is to estimate the response of humans to low doses based
on data derived from exposure of laboratory animals to high doses. This
approach is comprised of two quantitative estimations: first, interpola-
tion from responses obtained at high doses to estimate the response at
low doses within the test species and, second, extrapolation of the data
from the test species to estimate the response in humans.
Several mathematical models have been proposed to interpolate from
high to low doses within the test species (Scientific Committee of the
Food Safety Council, 1978; National Academy of Sciences, 1980a) . The
greatest uncertainty in these models is whether or not the kinetic char-
acteristics of the responses at high doses are similar to those at low
doses. This is a particularly important consideration when determining
whether there is a threshold. For example, is the risk directly propor-
tional to dosage level or is there a threshold dose below which the re-
sponse is negligible? Even though mechanistic arguments may be developed
in favor of a threshold effect (Gehring and Blau, 1977; see dose-response
curves in the report of Scientific Committee of the Food Safety Council,
1978), most mathematical models that have been used in the regulatory
process assume the nonexistence of a threshold for the general population
(National Academy of Sciences, 1980a). At the very least, were thresh-
olds to exist for individuals, there would undoubtedly be a distribution
of threshold values for which population parameters would need to be
estimated. That is considered impractical.
Assuming thresholds to be either nonexistent or unmeasurable , the
simplest mathematical model for high dose to low dose interpolation is
the linear dose-response model, wherein the response is directly propor-
tional to the dose at low levels of exposure. Mathematical models using
dose-response curves other than linear include the log-linear, log-norma]
and log-logistic models. Models based on "target theory," which are use<
for radiation-induced carcinogenesis, assume that the site of action has
18-4
a finite number of target sites that require some finite number of "hits"
to elicit a response (see review by Turner, 1975)* A more recent exten-
sion of this model was proposed by Cornfield (1977). According to the
Scientific Committee of the Food Safety Council (1978) , this model, in
which multiple hits are assumed and which has the strongest biological
foundation, provides a better description of dose-response data than the
single-hit model. This "gamma hit model" was found to fit dose-response
data for various types of toxic responses better than did some of the
simpler models (Scientific Committee of the Food Safety Council , 1978).
There is little support for and use of other models that mathemati-
cally describe a tolerance distribution, because they do not take into
consideration the multistep nature of chemical carcinogenesis (Finney,
1952). Some models (Druckrey, 1967; Peto et^ al. , 1972; Pike, 1966)
include additional parameters such as the time from initiation of expo-
sure to the development of tumor or, where there is no response , the
total period of observation. This period of observation would include
the time during which chemical modifiers would be expected to exert their
effects.
As mentioned earlier, the greatest difficulty with all of these
models is the interpolation of the response to low doses. Traditional
bioassays in animals are limited to the use of levels high enough to
produce an observable response. Virtually none of the data resulting
from such bioassays can be used to determine the most appropriate model
for interpolation to low doses. For example, even though similar risk
estimates were obtained from three common dose-response models (the log-
normal, log-logistic, and single-hit models) over a 256-fold experimental
dose range at relatively high doses, the projected risks at lower doses
were increasingly divergent (Food and Drug Administration Committee on
Protocols for Safety Evaluation, 1971). At a dose of 0.01%, which gave a
50% response, the single-hit model yielded a risk estimate 70., 000 times
higher than that obtained with the log-normal model.
Seriously compounding this uncertainty even further is the selection
of the most appropriate basis for expressing the dose. When more mean-
ingful comparative pharmacokinetic data are unavailable, it becomes nec-
essary to select a common unit to express the dose received by various
small, short-lived rodent species in order to compare that dose to the
dose received by humans. There is no unanimous agreement on whether to
express the dose as quantity per unit of body weight, body surface area,
or over a lifetime. To calculate the risk to humans from saccharin, the
Committee for a Study on Saccharin and Food Safety Policy (National
Academy of Sciences, 1978) compared results from four models for high
dose to low dose Interpolation (the single-hit, multistage, multihit, and
probit models) and expressed them as dose received from all three base
units (body surface area, body weight, and lifetime). The estimate of
risk derived from a Canadian study (Arnold et^ al. , 1980) ranged from
0.001 x 10~ 6 lifetime cases to 5,200 x 10~ 6 lifetime cases for ex-
posed individuals, a range of 6 orders of magnitude. Most of this var-
iance was attributable to the differing risks predicted by linear and
probit models.
18-5
The Office of Technology Assessment (OTA) of the U*S. Congress re-
cently issued a report on the assessment of technologies for determining
cancer risks from the environment (Office of Technology Assessment,
1981). Although this group accepted the nonthreshold extrapolation from
high dose measurements in animals to low dose estimates for humans, it
acknowledged that there can be as much as a fortyfold variation in the
risk estimate for low doses in humans, depending upon the scaling factor
used for determining the relationships between laboratory animals and
humans with respect to body size and rate of metabolism. Generally,
toxicologists adjust exposures for the differences in scale between spe-
cies on the basis of milligram per unit of body weight. This provides
the lowest estimate of risk to humans. When the experimental dose is
measured in parts per million (e.g., mg/kg diet, mg/cmr* air, or mg/
liter water) and humans are exposed through ingestion, the dose of the
chemical can be expressed as parts per million. This method is generally
used by the Food and Drug Administration (FDA) and, in some cases by the
Environmental Protection Agency (EPA), but it produces an estimate of
risk in humans 6 times greater than that estimated by the former method
if the mouse is the laboratory animal or 3 times greater if the rat is
used. Another method used by EPA takes the scale differences between
species into account and adjusts exposure on the basis of the relative
body surface areas of the test animal and humans. This gives a pro-
jected risk for humans 6 to 14 times higher than that of the first
method. The fourth approach is to adjust exposures on the basis of
relative body weight over a lifetime. This gives a projected risk
for humans 40 times higher than that of the first method.
An additional factor to be considered is the shape of the dose-
response curve. In general, linear interpolation provides the most
conservative estimate. This approach is used by most regulatory agencies
and is supported in the OTA report (Office of Technology Assessment,
1981).
The ultimate choice of a model for high to low dose interpolation is,
therefore, arbitrary. Not only is there great uncertainty in the mathe-
matical modeling procedures, but also there is no sound biological basis
for any of them (Scientific Committee of the Food Safety Council, 1978).
The Safe Drinking Water Committee concluded that the most suitable model
may be the multistage model because of the multistep nature of carclno-
genesis and because of the model's relatively conservative estimate of
risk (National Academy of Sciences, 1980a). The committee sees no reason
to modify that conclusion except to suggest that it should be reserved
for initiators of carcinogenesis and that there should be awareness of
the large variability among the heterogeneous human population.
MODIFIERS OF CARCINQGENESIS
For modifiers of carcinogenesis a different approach may have to be
considered. There have been few systematic attempts to assess the risk
18-6
for such compounds. However, the models discussed above may provide some
leads to potentially useful approaches, such as time to tumor response,
originally defined as the latent period by Armitage and Doll (1961). For
example, experiments using doses of the Initiator producing a high tumor
response would be useful in studying dose-dependent effects of negative
modifiers; conversely, experiments that produce barely perceptible re-
sponses could be used to examine dose-dependent responses of enhancers of
carcinogenesis. Although more data are needed to develop this concept,
several investigators have proposed specific mathematical models that
Incorporate time to tumor response (Druckrey, 1967; Peto et_ a^. , 1972;
Pike, 1966). Moreover, continuous exposure to a "carcinogen" Is con-
sidered in some models and time to tumor response has been incorporated
as a function of dose in order to yield the age-specific incidence rate
(Armitage and Doll, 1961; Crump, 1978; Hartley and Sielken, 1977).
Although the time to tumor response may have considerable hypothetical
and experimental utility for modifiers of carcinogenesis, such models
are severely limited for use in population-based studies because of the
unknown contribution and variable distribution of initiators.
Furthermore, withdrawal of an initiator may intercept progression of
carcinogenesis (Boutwell 1964; Sivak, 1979; Teebor and Becker, 1971).
Halving the dose-dependent progression of carcinogenesis should decrease
the final response by that amount, regardless of when such interception
occurred (Peto et^ ail. , 1981).
The Safe Drinking Water Committee concluded that conventional risk
extrapolation methodology accompanied by sufficient data and reasonable
models would predict risk to humans from studies in animals using low
doses with a precision varying from 1 to 2 orders of magnitude (National
Academy of Sciences, 1980a). Because of the differences in individual
susceptibility, the precision may, in fact, be much less.
USE OF MUTAGEN1CITY TESTS
As discussed in Chapter 3, the estimation of risk to humans from
exposure to mutagens Is beset with uncertainties. First, it Is difficult
to determine the dose of such substances In the diet. For example, the
general population may eat small or very small amounts of some extremely
strong mutagens (e.g., afiatoxin B^) and large quantities of certain
weak mutagens (e.g., flavonoids in vegetables), and the capability of our
biological defense mechanisms to protect us from either of these is not
well understood. Presumably, the effects of such exposure will be a
function of potency and dose, both of which extend over a very wide
range. To translate the product of potency and dose for a specific muta-
gen into an estimate of absolute risk for a human population, it is nec-
essary to know how to convert the values of mutagenicity obtained in
18-7
simple test systems into estimates of carcinogenicity. Unfortunately, no
way has been found to predict the carcinogenicity of any specific muta-
gen. One of the major difficulties in attempting such a determination is
the known interspecies variation in susceptibility to the effect of car-
cinogens and mutagens. Until the variables that control susceptibility
are better understood, it is impossible to extrapolate from tests for
mutagenicity to obtain estimates of carcinogenicity in humans. There-
fore, mutagenicity tests, which usually detect initiators, can be used
only as qualitative indicators of possible carcinogenicity. In the
absence of evidence derived from epidemiological studies, it is not
possible to estimate the likelihood that such substances will affect the
occurrence of cancer in humans.
USE OF EPIDEMIOLOGICAL STUDIES
Chapter 3 describes the approach used in epidemiological studies to
assess the importance of exposures to carcinogens or risk factors such as
diet or dietary components. The risk that disease will occur in humans
during a given time period is measured by the incidence of that disease.
Incidence can be accumulated over a lifetime in a population to measure
cumulative incidence, which is approximately equivalent to the lifetime
risk of disease (Day, 1976).
In cohort studies, the incidence of disease is measured directly:
the ratio of incidence in exposed and unexposed cohorts provides a
measure of the relative risk. The difference in incidence of disease
between exposed and unexposed groups provides a second measure of
risk the attributable risk, which is simply the proportion of disease
that can be attributed to the exposure to that particular variable, if
it is causal. Such measurements of risk are valid only if the two popu-
lations compared differ only by the exposure (variable) being studied
and if other factors influencing the risk of disease are controlled in
the analysis. The derivation of the attributable risk is dependent on
the reasonable assumption that the exposed group would have had an
incidence similar to that of the unexposed group if it had not been
exposed.
In case-control studies, estimates of the relative risk can be de-
rived. A large body of statistical and epidemiological literature has
accumulated to confirm that the odds ratios derived from case-control
studies are approximately equivalent to the relative risk determined in
cohort studies. Indeed, the same terminology is normally used in both
types of studies. Estimates of population-attributable risk can also be
derived from case-control studies. Such estimates are equivalent to
those expected in the general population, provided that the cases and
the controls are representative of their respective target populations
so that estimates of exposure in the population can be derived from the
control series.
18-8
These estimates of risk do not take into account the extent to which
risk may vary with age. Almost invariably there is a latent period be-
tween first exposure and the expression of a risk* For many diseases,
risk may appear to remain constant with age, but risk may decrease in
older groups because the population may have lost most persons suscepti-
ble to the effect, especially if a risk factor or constellation of risk
factors is responsible for more than one disease and if these diseases
are relatively common in a population or because of a birth cohort effect
that is increasing * An additional complexity is that risk may vary in
populations because the extent of exposures to various risk factors may
vary with time. This may lead to different expectations of lifetime
incidence for different birth cohorts. In this respect, incidence among
different age groups during the same time period may not accurately
reflect the expected lifetime incidence in a population. For example,
there has been a decline in risk for tuberculosis in successive cohorts
in the United States. The risk for this disease in the present genera-
tion is largely restricted to elderly males. Another example is the
risk for lung cancer, which has been increasing with successive cohorts,
especially among males, so that cross-sectional incidence curves show
maximum risk at middle ages and declining risk at older ages. For cervi-
cal cancer, there have been complex birth cohort effects. For example,
those who were in their twenties during the depression years show a low
incidence of cervical cancer, whereas others, particularly those who are
now in their twenties, appear to have a higher incidence. Thus, it is
difficult to interpret trends in incidence. However, for most of the
cancers believed to be influenced by diet and nutrition, the incidence
has been relatively stable for many years. Therefore, estimates of the
proportion of these cancers attributable to dietary factors are not
likely to be severely in error because of differences in risk encountered
by different birth cohorts.
Because the causation of cancer is often multifactorial, the summa-
tion of estimates of the percentage of cancers attributable to individual
factors often exceeds 100%. However, this does not invalidate the con-
cept. Rather, it indicates that it may be possible to adopt different
approaches to preventing a number of cancers.
DIET-RELATED CARCINOGENES1S
Given the limitations of traditional methods of risk assessment using
data from experimental and epidemiological studies, what factors would be
the most appropriate to consider in analysis of risk for diet-related
carcinogenesis?
Because food contains both initiators and modifiers of carcinogene-
sis, there is a need for two very different kinds of risk analysis. For
the initiators (mostly nonnutritive components of food), the Safe Drink-
ing Water Committee's conclusion that a multistage mathematical model
18-9
would be most appropriate (National Academy of Sciences, 1980a) is still
considered to be valid. For the modifiers in food (including nutrients
and nonnutritive substances), a mathematical model that includes time to
tumor response may be preferable. For enhancers, an experimental titra-
tion of a dose of the modifier, which has a potency for increasing a
near-zero tumorigenic response, may be an acceptable approach. Con-
versely, for inhibitors, tittation of the dose of the modifier with the
potency for eliminating nearly 100% of the response may be preferable.
Any experiment to determine the carcinogenic response to a dose of a
nutrient will be specific for the initiator, species, diet, and other
experimental variables used in the test.
Caution will have to be exercised when extrapolating the resultant
data to humans. In general, such extrapolation should Initially be
limited to qualitative rather than to quantitative conclusions* Greater
confidence in the initial results may be gained by testing more initia-
tors, species, and diets. The necessity for testing additional diets
arises from the knowledge that, there is an extremely broad array of nu-
trient-nutrient interactions. Thus, these reactions must be considered
when selecting the new diets to be tested.
As new data become available, it may become possible to do more quan-
titative extrapolation from the test species to humans with respect to
the risk from nutrient intake. The specific dose-response relationship
for the effects of nutrients on carcinogenesis will necessarily be limit-
ed by the requirement for nutrients for metabolic functions. This sug-
gests, therefore, that "risk" from nutrient intake should be defined In
terms of the Recommended Dietary Allowances (RDA) (National Academy of
Sciences, 1980c).
Beginning with the RDA's as the point of reference, the "risk" for a
nutrient could be defined In terms of RDA multiples (or fractions there-
of) . This approach would introduce a broader perspective Into the inter-
pretation of the "carcinogenic" effects of nutrients. It would acknowl-
edge that nutrients are essential and admit the existence of some level
of risk, even if that risk were negligible. The dose-response slope
constants will undoubtedly differ for various nutrients, and acceptable
upper limits of Intake, however arbitrary, will vary broadly as functions
of the RDA's for different nutrients. Analogous phenomena for noncar-
cinogenic toxicity of nutrients have been evaluated elsewhere (Campbell
et aiU , 1980; National Nutrition Consortium, 1978).
The Food and Nutrition Board's most recent edition of the Recommended
Dietary Allowances (National Academy of Sciences, 1980c) provides ranges
of intake for three vitamins and six minerals, the upper limits being
defined as "safe" on the basis of available Information. But, It Is
clear that epidemiologlcal studies will be needed to confirm or deny
whatever risk estimates for nutrient Intake may be obtained from experi-
ments In animals.
18-10
Doll and Peto (1981) suggest that laboratory data may be used for
setting priorities for regulation. However, they point out that even
tests in animals are unreliable, suffering not only from random errors,
but also probably from large systematic errors of unknown direction and
magnitude. Since there are thousands of chemicals that affect carcino-
genesis to some extent or other, in one laboratory test or another, it
is difficult to determine what, if any, practicable regulations should
be enacted on the basis of laboratory tests. Nevertheless, they suggest
that an appropriate use of results from laboratory tests might be to
estimate risk for humans by multiplying the potency of each chemical
studied by estimates, however crude, of the degree to which humans are
exposed to that chemical. This would yield an index of risk for humans.
Resultant estimates might provide a basis from which priorities for regu-
latory action could be determined.
There is one major difficulty with this approach. Although experi-
mental or epidemiological studies may have identified risk factors as
either potentially hazardous or protective for humans, it is difficult to
label many of them as carcinogens or modifiers of carcinogenesis.
Furthermore, even if such assessments were possible, the feasibility of
modifying the diet of humans would have to be considered.
It is impossible to enact regulations pertaining to diet, except for
those few substances that clearly qualify as food additives, which are
currently regulated according to the provisions in the Delaney Clause
(see Section B). Thus, it may not be appropriate to assess priorities
for regulatory action at this time, especially since changes in the econ-
omy and in the sources of our food supply may well combine to impose
dietary changes upon us. The dietary changes now under way appear to be
reducing our dependence on foods from animal sources* It is likely that
there will be continued reduction in fats from animal sources and an
increasing dependence on vegetable and other plant products for protein
supplies. Hence, diets may contain increasing amounts of vegetable prod-
ucts, some of which may be protective against cancer. However, if it is
decided that changes have to be Instigated, we should consider reducing
exposure of the population to total dietary fat and increasing exposure
to protective substances such as those found in fruits and vegetables,
while ensuring the maintenance of an ideal body weight for height and
well-balanced but varied nutrition.
CONTRIBUTION OF DIET TO OVERALL RISK OF CANCER
Higginson and Muir (1979) estimated the proportion of cancers related
to various aspects of the environment. They believed that precise pro-
portions of cancer incidence could not be attributed to diet, but they
did include dietary factors among the general heading "Lifestyle." They
estimated that possibly 30% of cancers in men and 60% in women in the
18-11
Birmingham and West Midland regions of England and Wales could be attrib-
uted to lifestyle. Wynder and Gori (1977) were more specific. On the
basis of international and intranational comparisons of cancer incidence,
the differences between U.S. mortality rates and the lowest reported
worldwide mortality rates for each site, and results of specific case-
control studies, they concluded that a little more than 40% of cancers in
men and almost 60% of cancers in women in the United States could be
attributed to dietary factors.
Using a similar approach, Doll and Peto (1981) were somewhat more
cautious. They agreed that a substantial proportion of cancers In both
sexes in the United States was likely to be attributable to dietary fac-
tors, but, by surveying the literature, they provided a rather wide range
of estimates (i.e., 10% to 70%) for the proportion of deaths from cancer
that could be reduced by practical dietary means. They stated that it
might not be possible to achieve a large reduction in the near future,
but that dietary modifications might eventually result In a 35% reduction
of deaths from cancer in the United States. This reduction was estimated
to include a 90% reduction In deaths from cancers of the stomach and
large bowel; a 50% reduction In deaths from cancers of the endometrium,
gallbladder, pancreas, and breast; a 20% reduction in deaths from cancers
of the lung, larynx, bladder, cervix, mouth, pharynx, and esophagus; and
a 10% reduction in deaths from other sites. These investigators placed a
greater degree of confidence in the projected 35% reduction in overall
mortality than in the estimated contribution from specific groups of
cancer sites.
Only two case-control studies of dietary factors and cancer provided
estimates of the proportion of cancers at specific sites that are attrib-
utable to dietary factors* On the basis of a case-control study of
breast cancer in Canada, Miller (1978) estimated that 27% of the risk of
breast cancer for women was attributable to total dietary fat Intake.
For colorectal cancer, Jain e ad. (1980) estimated that 41% of the risk
for males and 44% of the risk for females was attributable to saturated
fat intake. Both of these estimates are probably too low, because arti-
facts in the diet tend to lead to low estimates of relative risk
(Marshall e a^. , 1981). This is particularly true for breast cancer,
since estimated effects of dietary factors based on current Intake are
likely to be substantially below the true effect for a factor that is
operational earlier in life, possibly during adolescence.
The evidence reviewed by the committee suggests that cancers of most
major sites are influenced by dietary patterns. However, the committee
concluded that the data are not sufficient to quantitate the contribution
of diet to the overall cancer risk or to determine the percent reduction
in risk that might be achieved by dietary modifications.
18-12
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GLOSSARY
Acceptable daily intake (ADI): The daily dosage of a drug or a chemical
residue that appears to present no appreciable risk to health during
the entire lifetime of a human being.
Age-adjusted cancer incidence or mortality: The incidence or mortality
rate for cancer, adjusted for differences in the age distribution of
the populations being compared, i.e., the study population and a
standard reference population.
Anticarcinogen: A substance that inhibits or eliminates the activity
of a carcinogen.
Antimutagen: A substance that inhibits or eliminates the activity of a
mutagen.
Antioxidant: A substance that retards oxidation. Examples include
vitamin C, vitamin E, and butylated hydroxyanisole (BHA).
Benign tumor: A tumor that is confined to the territory in which it
arises, i.e., it does not invade surrounding tissue or metastasize
to distant organs. These tumors can usually be excised by local
surgery.
Bioassay: A test in which living organisms are used.
Cancer: Any of the various types of malignant neoplasms. See malignant
tumor, neoplasm.
Carcinogen: A chemical, physical, or biological agent that increases the
incidence of cancer.
Carcinoma: Cancer in an epithelial tissue, including external epithelia
(mainly skin and linings of the gastrointestinal tract, lungs, and
cervix) and internal epithelia (which line glands such as the breast,
pancreas, and thyroid).
Cocarcinogenesis : A general term that refers to augmentation of tumor
induction.
Cohort: 1. A group of people with a defined history of exposure who
are studied for a specific length of time to determine cancer in-
cidence or mortality. 2. A group of individuals born within the
same time period (usually within 5 or sometimes 10 years of each
G-2
other). Such groups are called "birth cohorts*" The diseases
among individuals in one birth cohort followed throughout their
lifetimes may be different from those in another, implying
differences in exposures to factors causing disease.
Complete carcinogen: An agent that can act as both initiator and
promoter .
Comutagen: A nonmutagenic substance that enhances the activity of
a mutagen or imparts mutagenic activity to another nonmutagenic
substance.
Contaminant: A substance that is present in foods or feed but is
not intentionally added.
Delaney Clause: Legislation passed by the U.S. Congress in 1958 that
forbids the addition to food any additives shown to be carcinogenic
in any species of animal or in humans*
Diet: The total composition of ingested food, including nutrients,
naturally occurring contaminants, and additives.
Dietary factors: Substances that are present in or characteristics
that are associated with the diet; for example, the amount of total
fat, dietary fiber, the ratio of saturated versus unsaturated fat,
and the method of cooking.
Environment: Anything external to humans, i*e., lifestyle factors and
anything to which humans are exposed, including all forms of radia-
tion and substances eaten, drunk, and inhaled. See lifestyle f actors
Epidemiology: The study of the distribution of diseases and their
determinants in human populations.
Epigenetic: As used in reference to cancer, an effect that does not
directly involve a change in the sequence of bases in DNA.
Dietary fiber: Generic name for plant materials that are resistant
to the action of normal digestive enzymes.
Food additive: Any substance that is added to food, either directly
or indirectly.
Food disappearance data or per capita intake. Crude estimates of food or
nutrients available for consumption by a specified population; based
on food production, imports, exports, etc. They do not reflect the
amount consumed since approximately 20% of the food is probably dis-
carded, wasted, or spoiled. In the absence of data on actual food
consumption, however, it may be the closest approximation of the per
capita dietary intake of that population.
G~3
Genotoxicity : The quality of being damaging to genetic material.
Hyperplasia : An Increase In the number of cells in a tissue or organ.
Incidence: The number of new cases of a disease expressed as a rate,
i.e., the number of new cases of a disease occurring in a given
population during a specific period, divided by the total number of
persons at risk of developing the disease during that same period.
Initiator: An external stimulus or agent that produces a cell that
can become malignant under certain conditions. Initiation events may
be mutational changes In a cell's genetic material, where the change
Is initially unexpressed and causes no detectable alteration in the
cell's growth pattern. The change Is considered to be irreversible.
Latency or latent period: The interval between the first exposure
to a carcinogenic stimulus and the appearance of a clinically
diagnosable tumor. For a disease like cancer, which usually
involves a sequence of steps over a long period, the term
"latent period" may be ambiguous.
Leukemia: Cancers of the blood-forming organs, characterized by
abnormal proliferation and development of leukocytes (white
blood cells) and their precursors In the blood, lymph, bone
marrow, and lymph glands.
Lifestyle factors: Identifiable and quantifiable parameters of living
(e.g., diet, smoking, drinking, hobbies) that are useful In
distinguishing population groups for epldemiologlcal studies.
Lymphoma : A cancer of cells of the immune system (e.g., lymphocytes),
where the tumor is confined to lymph glands and related tissues,
such as the spleen.
Malignant tumor: A tumor with the potential for Invading neighboring
tissue and/or metastasizing to distant body sites, or one that has
already done so.
Melanoma: Malignant melanoma is a cancer of the cells that produce the
pigment melanin.
Menarche: The age at which menstruation begins.
Metaplasia: The abnormal transformation of an adult (mature), fully
differentiated tissue of one kind into differentiated tissue of
another kind.
Metastasis : The spread of a malignancy to distant body sites by cancer
cells transported in blood or lymph circulation.
G-4
Modifier: A substance that can alter the course of carcinogenesis.
Morbidity: The condition of being diseased, or the incidence or
prevalence of some particular disease . The morbidity rate is
equivalent to the incidence rate.
Mortality: The number of overall deaths, or deaths from a specific
disease, usually expressed as a rate, i.e., the number of deaths
from a disease in a given population during a specified period,
divided by the average number of people exposed to the disease and
at risk of dying from the disease during that time*
Mutagen: A chemical or physical agent that interacts with DNA to cause
a permanent, transmissible change in the genetic material of a cell-
Multiple myeloma: A malignant neoplasm of plasma cells usually arising
in the bone marrow. Also called myelomatosis.
Neoplasm: A new growth of tissue with the potential for uncontrolled
and progressive growth. A neoplasm may be benign or malignant.
Nutrient: A component of food (e.g., protein, fat, carbohydrates,
vitamins, minerals) that provides nourishment for growth and
maintenance of the organism.
Nutrition: The sum of the processes by which an organism utilizes the
chemical components of food (which may or may not be synthesized ijn
vivo) through metabolism to maintain the structural and biochemical
integrity of its cells, thereby ensuring its viability and repro-
ductive potential.
Papilloma: A benign epithelial neoplasm.
Per capita intake : See food disappearance data.
Permissible residue: The quantity of a residue (e.g., a pesticide
residue in or on a food crop) permitted when the product is
first made available for consumption. The value may be calculated
from the ADI ( See acceptable daily intake) .
Precancerous lesion: A lesion or visible abnormality that has a
significant probability of later developing into cancer.
Prevalence (point prevalence): The number of existing cases of a dis-
ease, usually expressed as a proportion, i.e., number of cases of
a disease in a given population at a specified time, divided by the
estimated number of eligible persons in the population at that same
time.
G-5
Promoter : An agent that causes an initiated cell to produce a tumor
after prolonged exposure. Promotion events or, more generally, late
events can occur only in "initiated" cells and are somewhat reversi-
ble* Discontinuation of exposure to a promoter before tumor develop-
ment may prevent the appearance of a tumor .
Pyrolysis: The decomposition of a substance by heat.
Recommended Dietary Allowance (RDA) : The level of intake of essential
nutrients that is adequate to meet the nutritional needs of
practically all healthy persons, as judged by the Committee on
Dietary Allowances of the Food and Nutrition Board, National
Research Council.
Risk: As used in epidemiological sections of this report, risk refers to
the probability of occurrence of a disease (cancer) in a given
population.
Relative risk: An estimate obtained by dividing the Incidence of cancer
in the exposed group by the incidence in the corresponding unexposed
or control group.
Sarcoma: Cancers of various supporting tissues of the body (e.g., bone
cells, blood vessels, fibrous tissue cells, muscle).
Synergism: When two or more substances enhance each other's effects,
achieving more than the sum of their individual effects.
Threshold dose: A non-zero dose below which exposure Is safe and not
associated with risk.
Tolerance level: The maximum level or concentration of a drug or
chemical that Is permitted in or on food at a specified time
during slaughter (or harvesting), processing, storage, and
marketing up to the time of consumption by an animal or human
being.
Transformed cell: A cell that has undergone both initiation and
promotion and has the potential for leading to the develoment of
a neoplasm.
Tumor: An uncontrolled and progressive growth of tissue. A neoplasm.
It encompasses both benign and malignant neoplasms, but occasionally
may refer merely to a swelling of tissue.
Unintentional residue or contaminant : The residue of a compound in
feed or food resulting from circumstances not intended to protect
the feed or food against attack by infectious or parasitic diseases.
The residue may be acquired during any phase in the growth, produc-
tion, processing, or storage of feed or food.
APPENDIX A
COMMITTEE ON DIET, NUTRITION, AND CANCER
AFFILIATIONS AND MAJOR RESEARCH INTERESTS
CHAIRMAN;
Clifford Grobstein
Professor of Biological Sciences
and Public Policy
University of California
San Diego, Calif.
Major Interests: Developmental
biology and biomedical tech-
nology assessment
VICE CHAIRMAN;
John Cairns
Professor
Department of Microbiology
Harvard School of Public
Health
Boston, Mass.
Major interest; Molecular biology
MEMBERS :
Robert J. Berliner
Dean
Yale University
School of Medicine
New Haven, Conn.
Major interests; Physiology of
the kidney, particulary with
respect to fluid and electrolyte
transport
Selwyn A. Broitman
Assistant Dean and Professor of
Microbiology and Nutritional
Sciences
Department of Microbiology
Boston University School of
Medicine
Boston, Mass.
Major interests; Intestinal
microflora and experimental
gastroenterology
MEMBERS (CONTINUED)
T. Colin Campbell
Professor of Nutritional
Biochemistry and
Director of Nutrition and
Cancer Program Project
Division of Nutritional
Sciences
Cornell University
Ithaca, N.Y.
Major Interests: Mechanisms
of nutrient effects on
chemical carcinogenesis, af la-
toxin-induced hepatocarcino-
genesis, and carcinogen metabolism
Joan Dye Gussow
Chair
Department of Nutrition Education
Teachers College
Columbia University
New York, N.Y.
Major interests: Social and
technological changes affecting
the human food chain
Laurence N. Kolonel
Director
Epidemiology Program,
Cancer Center of Hawaii and
Professor of Public Health
University of Hawaii
Honolulu, Hawaii
Major Interest: Cancer epidemiology
David Kritchevsky
Associate Director
Wistar Institute
Philadelphia, Pa.
Major Interests: Lipid metabolism
and atherosclerosis
A-2
MEMBERS (CONTINUED);
Walter Mertz
Director
Human Nutrition Research Center
Agricultural Research Service
U.S. Department of Agriculture
Beltsville, Md.
Major interests: Nutrition and
trace elements
Anthony Bernard Miller
Director
National Cancer Institute of Canada
Epidemiology Unit and
Professor
Preventive Medicine and Biostatis-
tics
Division of Community Health
University of Toronto
Toronto, Canada
Major interest: Cancer epidemiology
Michael J. Prival
Research Microbiologist
Genetic Toxicology Branch
U.S. Food and Drug Administration
Washington, D.C.
Major interest: Mutagenicity testing
using bacteria
Thomas Joseph Slaga
Senior Staff Member
Biology Division
Oak Ridge National
Laboratory
Oak Ridge, Tenn.
Major interests: Chemical
care inogene sis, pharma-
cology, biochemical endo-
crinology, and gene
regulations
MEMBERS (CONTINUED):
Lee W. Wattenberg
Professor
Department of Laboratory
Medicine and Pathology
University of Minnesota
Medical School
Minneapolis, Minn.
Major interests: Chemical
carcinogenesis and chemo-
prevention
ADVISOR:
Takashi Sugimura
Director
National Cancer Center
Research Institute, Tokyo, and
Professor, Institute of Medical
Sciences
Tokyo University
Tokyo, Japan
Major interests: Chemical
carcinogenesis and bio-
chemistry
NATIONAL RESEARCH COUNCIL STAFF:
Sushma Palmer
Project Director
Assembly of Life Sciences and
Adjunct Assistant Professor
of Pediatrics
Georgetown University
School of Medicine
Washington, D.C.
Major interests: Nutrition,
growth and development,
and nutrition and immune
response
A-3
NRG STAFF (CONTINUED);
Kulblr Bakshi
Staff Scientist
Assembly of Life Sciences and
Adjunct Graduate Assistant Professor
Howard University
Washington, B.C.
Major interest: Chemical
mutagenesis
Robert Hilton
Research Associate
Assembly of Life Sciences
Washington, D.C*
Major interest: General biology
Frances Peter
Editor
Assembly of Life Sciences
Washington, D.C.
Major interest: Scientific
communication
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